Robin van Persie's last-gasp goal rescued a point for Manchester United as Louis van Gaal and Chelsea manager Jose Mourinho shared a 1-1 draw.
The Portuguese looked to be heading for a famous victory against his one-time mentor at Barcelona after Didier Drogba's second-half strike had given Chelsea the lead.
But deep into injury time – and after Branislav Ivanovic had been sent off for a second bookable offence – Van Persie pounced on a half-cleared free-kick to smash home an equaliser.
The point means that Chelsea's lead at the Barclays Premier League summit is now four points over Southampton, while they are six points better off than Manchester City following the defending champions' 2-1 defeat at West Ham United on Saturday.
Marouane Fellaini was rewarded from his goalscoring appearance in United’s recent 2-2 draw with West Bromwich Albion with a start in midfield at the expense of Ander Herrera, while Chris Smalling replaced the injured Phil Jones at centre-back.
Diego Costa and Loic Remy missed out for Chelsea due to a virus and a groin problem respectively, meaning Drogba played as their attacking spearhead.
There was a full league debut for Filipe Luis as regular left-back Cesar Azpilicueta began a three-match suspension.
Van Persie led the United attack alone as suspension and injury deprived Van Gaal of Wayne Rooney and Radamel Falcao, and the Dutch striker had his first clear opening in the 23rd minute.
Adnan Januzaj's through-ball was threaded through the Chelsea backline but goalkeeper Thibaut Courtois was out quickly to block Van Persie's effort.
Marcos Rojo and Smalling were fortunate not to be penalised for wrestling John Terry and Ivanovic to the ground in the penalty area from a 36th-minute free-kick and Argentina international Rojo continued a shaky start when his error allowed Drogba to test David de Gea.
Playing against his former club, Juan Mata was afforded plenty of room when Angel Di Maria slid a free-kick towards him in first-half stoppage time, but the Spain playmaker shot woefully off target.
Fellaini fired narrowly wide from the edge of the box under pressure at the start of the second half, but Chelsea found the opening goal in the 53rd minute.
After Eden Hazard had cut in from the left flank and exchanged passes with Drogba to draw a superb save from De Gea, the veteran striker escaped Rafael Da Silva's attentions at the near post to head in the resulting set-piece.
Right-back Ivanovic again made his presence felt in the United area with a storming 69th-minute run but pulled his shot wide from an acute angle.
Courtois denied Van Persie with his legs in the 79th minute but the same player gave the Old Trafford faithful a timely reminder of the late drama of the Alex Ferguson years by levelling the match deep into stoppage time.
Ivanovic earned his red card for bringing down Di Maria, who picked himself up to deliver an excellent free-kick.
Courtois saved well from Fellaini's header initially, although he was helpless as Van Persie slammed home the rebound to send Van Gaal's men into next weekend's derby against City in high spirits.
Manchester United manager Louis van Gaal: "I said to the boys it was not our best performance and that's a pity because at this moment you have to show yourself against the better teams. But despite that we have created a lot of chances, much more than Chelsea. Chelsea has created one chance in the first half and before the goal they had the chance of [Eden] Hazard] that [David] De Gea stopped fantastically. From the corner kick there was a lack of communication and that's why they scored. That is always the difference in such games. After that we lost our head for 10 or 15 minutes and they could have scored a second goal."
"Chelsea tried to kill the game with ball possession and making the pitch big so we have to run a lot. But my boys did that - they ran, they fought to the end and in the end we scored. I thought it was very, very deserved. "We have created a lot of chances also but we didn't finish well. We could have killed the game before half time but we didn't and then they scored - then you know Chelsea are the best club in Europe at killing the game. Nevertheless we created one or two chances and we scored the goal."
Chelsea manager Jose Mourinho: " My feeling is that we had a good first half and a fantastic second half. To come here and not to be happy with the point, because we are not, shows clearly how good we were and how well we are playing at this moment. I am so happy with my players. We got the same result as last season here but if I compare what we did last season and what we did this season it shows clearly the evolution of this team.
"We are not happy with a point. This is only possible when you play so well and feel that you are so good not to be happy with a point at Old Trafford. I am really happy with the players individually and the team as a team."
"Manchester United have one of the best managers in the world. When you have one of the best it is not easy to get one better. He is one of that group. He is a great coach, a great manager. They are in great hands. Louis, with time, will make a fantastic team."
|02 Dec 2014||v Stoke (H)|
|20 Dec 2014||v Aston Villa (A)|
|14 Dec 2014||v Liverpool (H)|
|22 Nov 2014||v Arsenal (A)|
|08 Nov 2014||v Crystal Palace (H)|
|08 Dec 2014||v Southampton (A)|