Arsenal's Premier League title challenge suffered a massive blow as the 10-man Gunners were beaten 1-0 at home by lowly West Ham on Saturday.
Jarrod Bowen headed in the only goal just before halftime and an injury-hit Arsenal had no reply after Myles Lewis-Skelly was sent-off on 73 minutes.
Defeat leaves second-placed Arsenal still eight points adrift of leaders Liverpool.
The Reds can extend that advantage to 11 when they visit a diminished Manchester City on Sunday.
Any pressure that had built up on Liverpool after drawing two of their last three Premier League games was eased as Arsenal failed to cope with an injury crisis that has depleted Mikel Arteta's attacking options.
Midfielder Mikel Merino stepped up in the absence of Kai Havertz, Gabriel Martinelli, Gabriel Jesus and Bukayo Saka with a late double to beat Leicester 2-0 last weekend.
However, the Hammers easily snuffed out the Spaniard and secured just a second win since Graham Potter took charge seven games ago.
Bowen applied the finishing touch for the winner, but the goal owed more to a driving run and pinpoint cross from Aaron Wan-Bissaka which caught the Arsenal defence off guard on 44 minutes.
The home side then left themselves a mountain to climb with a fifth Premier League red card of the season.
Lewis-Skelly has received two of them. The teenager was also sent-off in last month's 1-0 win at Wolves.
That decision was overturned on appeal, but the left-back could have few complaints this time despite referee Craig Pawson initially only brandishing a yellow card after Lewis-Skelly hauled down Mohammed Kudus.
After a VAR review, Pawson upgraded the yellow to a red for denying of a clear goalscoring opportunity.
West Ham should have added to their lead late on when Kudus and Evan Ferguson failed to beat David Raya.
It did not matter as Arsenal's toothless attack could not break the visitors down in what may prove the death knell for their chances of a first league title since 2004.