Manchester United goalkeeper David De Gea produced another blunder to gift Chelsea a 1-1 draw in the battle between the two top four hopefuls.
Ex-Chelsea man Juan Mata had given the hosts an early lead at Old Trafford, but Maurizio Sarri's men were level just before half-time when De Gea spilled Antonio Rudiger's long-range effort into the path of Marcos Alonso, who made no mistake.
Defeats for Tottenham and Arsenal this weekend meant the winner of this clash had the chance to steal a march on their rivals.
United boss Ole Gunnar Solskjaer named Ander Herrera in his starting line-up, despite the Spanish midfielder believed to be close to joining Paris Saint-Germain in the summer.
United were on top and Lukaku showed his determination as he barged defender Cesar Azpilicueta into the advertising hoardings, but they failed to add to their lead and were pegged back on 43 minutes following another De Gea howler.
The Spain No. 1 has been at fault for goals against Arsenal, Barcelona and Manchester City in recent weeks.
Buoyed by that equalising goal, Chelsea were much brighter after the break, but failed to test De Gea's frail confidence further.
Both sides lost central defenders to worrying-looking knee injuries in the second period with Chelsea seeing Rudiger hobble off on 65 minutes and United's Eric Bailly following him down the tunnel six minutes later.
The result means Chelsea stay fourth but move two points clear of fifth-place Arsenal, with United a point further back in sixth.