A Cesc Fabregas goal on 11 minutes appeared to send the home side on their way to a comfortable victory in Group G but profligate finishing allowed the Germans to gain in confidence and their second-half reward came from the boot of striker Klass-Jan Huntelaar.
The return of Didier Drogba was a damp squib in terms of output but lack of match proactive would contribute to that.
Chelsea's best chance in the opening encounters fell on nine minutes to Ramires, but his powder-fluff left foot shot from just inside the German penalty area, dribbled toward the gleeful Ralf Fahhrmann, the visitors' goalkeeper.
But the dominant Blues would not be denied and took the lead two minutes later.
Cesc Fabregas appeared to foul Max Meyer, but referee Ivan Bebek allowed play to continue and Eden Hazard picked up the ball inched to wards the Schalke penalty area before clipping a reverse pass to the overlapping Fabregas on his left. The midfielder took one touch before sending a right-footer into to the back of the net - Fahrmann could only parry the ball over the goal line.
Striker Klass-Jan Huntelaar received a yellow card for his protestations at the apparent injustice.
Hazard almost doubled the lead as the home side cut through the Schalke defence at will.
But Marcos Hoger was on hand to kick, his goal-bound shot away for a corner.
Sidney Sam, looked the liveliest of the Germans and a couple of long-range efforts, while on target, failed to cause Thibaut Courtois any difficulties.
Kevin-Prince Boatang was next in Bebek's book for a cynical body check on unplayable Hazard on 25 minutes.
A fine ball by debutant Filipe Luis on 32 minutes found Didier Drogba and the Ivory Coast hit man directed a powerful header towards goal from just inside the Schalke area, but it wasn't wide enough to trouble Fahrmann who clutched the ball safely to his midriff.
Fabregas, had he took an extra touch, on 38 minutes as a byline cutback from Branislav Ivanovic rolled invitingly towards him, he would surly have scored his second. Instead, a slight panic ran through the ex-Arsenal man and he thrashed a sitter over the Schalke crossbar.
A minute later the Germans showed some mettle and and skill when setting up Boateng - the midfielder let free with a 25-yard rasper, that arrowed towards goal. Thankfully for the Chelsea faithful, Courtois stretched his 6ft 6in frame to dive to his right and parry the ball away from goal and for a corner.
Just before the break, Julian Draxler should have equalised as his mazy run cut right through the Chelsea rearguard. His final shot, a scuffed left-footer zipped across Courtois and wide of goal.
Neither side made any changes at half-time but the pattern of the first was been repeated - Chelsea on top, Schalke, threatening on the break.
Boateng does have a fizzler in his shooting leg and on 55 minutes produced a seemingly speculative 30-yarder that gathered pace as it headed towards Chelsea's goal.
Courtois had to take two touches of the ball before gathering control.
Skipper John Terry entered the ref's book for kicking the ball after play was stopped for a foul.
Drogba, making his first Champions League match for Chelsea since scoring the winning penalty in Munich in 2012, hustled his way clear but scuffed the ball wide.
A minute later on 62 minutes and Chelsea's fragility at the back was cruelly exposed when Fabregas gave the ball away in midfield.
It was picked up by Draxler who raced clear. He cut the ball across to his left to in-running Huntelaar. As the Chelsea rearguard moved backwards allowing the striker to get into the danger zone of the edge of the Chelsea penalty area, the German hit a right-footed daisy-cutter which squeezed past Courtois and his near post.
Jose Mourinho's response was almost instant, bringing on Oscar for Ramires.
That goal gave the visitors a lift and Chelsea's confidence took a beating. Draxler then tested Courtois with a long-range blaster on 69 minutes. Again Courtis was its equal.
Schalke boss Jens Keller brought on in Eric Maxim Choupo-Moting for Meyer while Mourinho, sensing the game slipping away took the brave move of bringing on, on 73 minutes, Diego Costa and Loic Remy - replacing Drogba and Willian.
The change almost reaped instant dividends when Remy got the ball after Fahrmann flapped at a deep Fabregas cross. But the Frenchman saw his angled shot cleared off the line from the head of Roman Neustadter.
Hazard was next up with the minutes ticking away, but his volley inched over the visitors's crossbar.
An outstretched lunge by Hazard on 83 minutes, from a deep Oscar pass, forced Fahrmann into a desperate and spectacular save to his right as the Blues went in search of a winner.
Nemaja Matic then saw his header cleared off the line by Christian Fuchs as the Blues laid siege on the Schalke goal.
But it was to no avail and a point was shared.
Teams, Chelsea, Courtois, Ivanovic, Luis, Fabregas, Ramires, Hazard, Drogba, Matic, Willian, Cahill, Terry
Subs, Cech, Zouma, Oscar, Mikel, Remy, Costa, Azpillicueta
Schalke 04, Fahhrmann, Meye, Boateng, Draxler, Hoger, Aogo, Sam, Fuchs, Ayhan, Hutelaar, Neustadter
Subs, Wetklo, Friedrich, Clemens, Choup-Moting, Obasi, Barnetta, Avdijaj
Ends
Gary Cahill, England deputy captain played his part in the 1-1 draw against Schalke last night but was feeling frustrated that the Blues did not kill off the game when they had the Germans reeling.
An 11th minute opener from Cesc Fabregas looked to have put the Chelsea in the box seat, but an inability to score from a host of chances was punished when Klas-Jan Huntelaar nabbed a 62nd minute equaliser.
"It feels a bit flat to be honest." Said a dejected Cahill.
"The other teams in the group drew but we had enough of the game in terms of chances to put the game to bed.
"They only hurt us when they broke on us. They did that a couple of times with a couple of chances."
Chelsea are top of the Premier League with the perfect four wins in a row. But with this draw they have have kept only one clean sheet,
But that is not bothering Cahill too much.
"We are not massively worried by that." He said.
"You can see that we are more attacking. The are a few more additions to our team but we would have liked to do more defensively, But if you average it out between now and the end of the season I'm sure it will be fine. As defenders we want to keep a clean sheet but we have had a great start to the season - not lost a game yet.
"We are feeling positive about the group. This Schalke side are better than when we played them last year, nevertheless we created a lot of chances. But all of a sudden they scored. The longer the game when on when it was one nil, there was a chance that they might get a break and that's what happened.
"But that football, but we should have seen the game out.
"We have been very attacking from the start of the season and we are working as a team to keep it tight like last season - we will get it right sooner or later," he said.
Friday piece
Chelsea face a doubting task of trying to see off Manchester City on Sunday in the 4pm kick-off game.
Keeping a clean sheet will be a priority on and is something that will be occupying the thoughts of Cahill and the rest of the side.
"To keep a clean sheet there will be easier said than done," said Cahill.
"But of course we are going to go the and give it a good go.We have started well, but unfortunatley for them they lost to a late goal in their Champions League match at Bayern Munch on Wednesday.
"It's is going to be an amazing game like it always is - two good teams going head-to-head at the top."
Cahill is well versed in playing right at the very top level for Chelsea and England and is relishing the task of locking horns with the best that City will throw at them.
"Players always like to play in these games," he said. "And they don't come too much better than this. From a neutral point of view it's going to be exciting and a good game, but it's also about trying to get the right result, but it will be very very tough."
Last year's one-nil victory at Man City when Branislav Ivanovic scored the winner was one of Chelsea's finest defensive and attacking shows of the season - will Chelsea fans be expecting something similar?
"I'm sure we will be working on things right up to kick-off, knowing the way the manager works," said Cahill.
"We will be fully prepared for that game, but with such good players you can never know what they will do, but we be ready, we are in good form. It won't be easy, but it's certainly a game to look forward to."
If Chelsea do win, then they will go nine points clear of their title rivals, will that be significant?
"If, if, it's if and buts," he suggested.
"But if we did win then we will be continuing our great start to the season, but I'll speak to you after the game to let you know how it went,
"I think they are title challengers, they are always going to be up their around the top, the last few seasons have proved that, they will be one of them."
Chelsea beat Man City home and away last season and psychologically that was not lost on Cahill.
"I don't like talking about the past," he said. "And what happened last season don't matter. when when we played them home and away last season we played fantastically well, and they found it tough.
"But we got a disappointing result in the FA Cup when we lost up there. It will be a tough game, they have world-class players, so result like like season will be amazing."
There is a chance that Chelsea legend Frank Lampard could turn out against Chelsea.
Lampard left the Blues last season and joined City on a six-month contract before starting his USA career in March.
"I'm sure our fans will give Frank a good exception if he played, " added Cahill.