Chelsea were booed off after they blew another lead at Stamford Bridge, with Wesley Fofana's red card and Zian Flemming's powerful header helping battling Burnley grab a precious 1-1 draw.
Liam Rosenior's Blues were in complete control, pushing for a second to add to Joao Pedro's early opener. But then their red-card problem struck again.
For an eighth time this season they were reduced to 10 when Fofana planted his studs into James Ward-Prowse's foot for a second yellow.
Tosin was lucky not to follow him back to the dressing room for a shove on Flemming when he got the wrong side of the centre-back.
But Flemming would have his big moment - capitalising on non-existent marking to head home Ward-Prowse's 93rd-minute corner.
"It is unacceptable for their best header of the ball to be free in the box," said a fuming Rosenior. "I am learning very quickly about this team and I know what needs to be done for us to improve."
Burnley may have suffered a bad FA Cup exit to Mansfield last weekend but this draw, on the back of their comeback win at Crystal Palace last time out in the league, shows the second-bottom side are still fighting. Their gap to survival is now eight points.
Chelsea, though, were masters of their own downfall. After Sunderland and Leeds came from behind here earlier in the season, Burnley have completed the set for promoted sides battling back for rewards at Stamford Bridge. Crucial points Chelsea could count the cost of come the end of the season.
"It is too many times," rued Rosenior. "It is not enough clean sheets and not enough basic and values of defending set-pieces. That is something l have to address.
"There were players on the pitch who were assigned to do their job and who didn't do their job. That is what cost us the two points."
Chelsea are up to fourth but away games with Arsenal and Aston Villa next, their Champions League qualifying hopes have taken a hit. Their fans were not impressed.
Chelsea had got off to a flying start, with in-form Joao Pedro sliding in his seventh goal in his last nine games after Pedro Neto got in behind Kyle Walker.
Walker and Joe Worrall put in blocks to prevent Cole Palmer adding a quick second and, although Burnley got a foothold, they were relieved to see Palmer spurn a one-on-one chance after a bad Walker error. The out-of-sorts Walker was hooked at half-time.
Burnley continued to put bodies on the line as Chelsea looked to reassert their authority after the break, with Worrall's excellent tackle on Palmer followed by Bashir Humphreys sliding in to prevent Joao Pedro adding to his tally.
Fofana's red completely shifted the mentality of both teams. Rosenior sent on Tosin for Palmer - who went down the tunnel for treatment - and could easily have seen the sub sent off too.
Chelsea's nervousness increased and the failure to pick up Flemming from that late corner was a basic error. Jacob Bruun Larsen almost added a winner from another corner moments later.
They do go above Man Utd in the standings but, ahead of United's trip to Everton on Monday Night Football, there will be plenty of scrutiny on the discipline of this young Chelsea team. They now have some huge games coming up to bolster their Champions League qualifying bid.
Chelsea boss Liam Rosenior:
"No, that wasn't on Wesley. That was on our performance. From the first goal, we lacked incision when we had control. I want incision. I want us to create wave after wave of attack. We were too safe in our possession.
"When you give a team, any team, a one-goal advantage, anything can happen. The red card happens, you're down to 10 men. We knew their biggest threat with Ward-Prowse on the pitch was set-plays. We went as big as we possibly could because that was the only way they could score with 10 men. We still don't see it out.
"I think the frustration is more the last two home games, from being in winning positions and being in control of the game, to not win the two games. That's the biggest frustration. It's not a blame on an individual."
Burnley boss Scott Parker:
"We've had a big challenge this year and at times we've fallen a little bit short in terms of levels or in terms of the quality. We've come into a big league and at times we've just fallen a little bit short on that. The one thing we have not fallen short on is the resilience that this group has shown tirelessly, tirelessly and tirelessly.
"This pressure has increased tenfold at times where it's come on top, and for such a young group, they bounce back. We keep fighting, we keep coming, and they get exactly the same today. So, I'm immensely proud of the boys and they deserve that."
