Meanwhile, Liverpool atone for their Capital One Cup defeat with victory over Manchester City
Five games for your delectation tonight in the Premier League and as the season winds down and heads for a close run-in, teams are beginning to rue dropped points.
After last night's 2-2 draw at home to West Brom, the knives were out for Leicester and the door swung open in favour of Tottenham.
A win tonight would have secured them top spot on goal difference, the first time they would have been top of the league outside of August since the start of the Premier League area.
Instead, West Ham put in an absolutely supreme performance. They pressed high up the pitch, stifling the attacking threat of Christian Eriksen and Harry Kane.
Tottenham were squeezed, stretched and looked out of ideas come the end of the first half. Michail Antonio's goal on seven minutes was all that was required to deny Mauricio Pochettino's side anything from the game.
Arsenal, meanwhile, have gone some way to proving Graeme Souness right with a 2-1 home defeat to Swansea.
Despite having gone ahead , they were hit back and Ashley Williams' second half goal eased the pressure on the Welsh side.
Without having to kick a ball this evening, Claudio Ranieri can breathe a sigh of relief that his side remain three points clear.
"Tottenham, in my opinion, are favourites" said the wily Italian before the round of fixtures.
Mind games? Surely not.
Mauricio Pochettino couldn't capitalise on Leicester's slip last night. Image: John Walton / PA Wire/Press Association Images
Suddenly, Manchester United are the form team. They've won their last two Premier League games, their last four in all competitions.
Ok, so two of those victories have been against FC Midtjylland and Shrewsbury Town, but to come off the back of those two games to beat Arsenal with a massively depleted squad deserves credit.
Four games in ten days is a lot for any team, especially one that has to manage resources carefully.
Tonight's victory over Watford, coupled with neighbours Manchester City's defeat to Liverpool, leaves them level on points with Manuel Pelligrini's side and tied for fourth position.
The Manchester Derby at the Etihad in 17 days time could have a serious baring on how the top four is shaped come May.
Keep in mind that City do have a game in hand, but insipid performances like tonight will give Louis van Gaal's men confidence that they can overtake their nearest rivals.
As of right now, momentum swings in favour of United, with first team starters on the cusp of return.
Juan Mata scored the only goal of the game in tonight's win over Watford. Image: Martin Rickett / PA Wire/Press Association Images
Adam Lallana sparkled tonight as Liverpool put a dent in Manchester City's Premier League hopes and exacted swift revenge for their League Cup penalty defeat on Sunday night.
Lallana, as well as James Milner and Roberto Firmino condemned Manuel Pelligrini's side to a defeat which leaves them fourth and level on points with Manchester United.
Their worrying slip in form has coincided with the announcement that Pep Guardiola will take over at the start of next season, with one win and three consecutive league defeats.
The Chilean manager is sticking diligently to his task in progressing City in the Champions League and (barring disaster) the team are on course for their first ever quarter-final in the competition.
"BOOM" said Jurgen Klopp after the game, the eccentric German delighted with what he described as his side's best home performance and result.
He was right to be excited about the display, Liverpool showed glimpses of the side they can be. What he needs to exact is the consistency of the performances.
But for now, with a game in hand, Klopp's men will take this victory and begin their march for a top-six finish.
Adam Lallana put in a virtuoso performance at Anfield this evening, getting his name on the scoresheet. Image: Peter Byrne / PA Wire/Press Association Images