An end-to-end first half somehow featured just one goal, with Konstantinos Mavropanos putting through his own net under pressure from Michael Kayode in the 15th minute.

Mavropanos had a powerful header at the other end disallowed for offside, while Valentin Castellanos struck both posts before the interval, with a curler from the edge of the box and a bullet header from a corner.

Igor Thiago and Mikkel Damsgaard also passed up excellent chances before the first period was through, but they were both on target in the second as Brentford streaked clear.

Thiago sent Mads Hermansen the wrong way from the penalty spot in the 54th minute, after El Hadji Malick Diouf clumsily chopped down Dango Ouattara just inside the area.

Damsgaard completed the scoring with a neat turn and finish with eight minutes to play, after the Hammers hit the woodwork for a third time when Crysencio Summerville's curler struck the crossbar.

While Brentford climbs three places to sixth, which could bring UEFA Champions League qualification if Aston Villa finishes fifth and wins the UEFA Europa League, the result is a major blow to West Ham's survival hopes.

It remains two points clear of Tottenham Hotspur in 17th, but will drop into the bottom three if Roberto De Zerbi's Spurs side beats Villa on Monday (AEST).

But West Ham boss Nuno Espirito Santo wants his side to remain together and only focus on its final three matches of the season.

"It's going to be a big challenge for all of us with the impact of this tough day," he said.

"It's up to us how we're going to react to this. We've got three games to go, and it's going to go to the wire.

"But that's what I said to the boys: 'Let's keep together, let's realise how we react from a bad day is going to keep us alive in the fight'."

Nuno was encouraged by how West Ham started the encounter.

"We played a very good first half," he said.

"We didn't achieve [a goal], we had chances with the post, and we created a lot of problems for Brentford.

"So, we were positive in the first half, but then [after they scored] the penalty in the second half, we lost a bit of composure and organisation, and it became much harder."

Brentford boss Keith Andrews was delighted with the way in which his side found a way to win.

"We probably haven't had what we deserved, but that's the game and the level that we're at," he said.

"I wanted us to find a way to win, most importantly, with just a few games to go until the end of the season.

"We've had a special season so far, and I really want us to continue to do that."