Gianluca Scammaca's late winner in Brussels was enough to ensure West Ham remain top of Conference League Group B with maximum points.But David Moyes' side - captained on the night by Angelo Ogbonna in the absence of Declan Rice - had Alphonse Areola to thank for maintaining that slender lead as the French stopper produced a wonder save six minutes from time.
The trip to Lotto Park was widely considered to be the toughest of West Ham's six group games, even though Anderlecht went into the game in indifferent form.
Yet the Hammers, who rested no less than eight players from the team that started against Wolves at the London Olympic Stadium last Saturday were still too strong for a side they last met competitively in the final of the Cup Winners Cup some 46 years ago.
The Hammers created 18 shots at goal during the game but tellingly, managed only five on target.
Said Benrahma and Michail Antonio, both seeking to boost their claim for a starting spot in Moyes' Premier League squad were most guilty of squandering good chances, with the Algerian enjoying no fewer than five attempts at goal before the break.
The best of those fell to Benrahma five minutes ahead of the break when Jarrod Bowen's low centre left him with the goal at his mercy - only for the winger to scoop his shot over the bar from just seven yards out.
At the other end the hosts had rarely threatened Areola's goal but they should've gone ahead two minutes after Moyes made a triple substitution, when he introduced Declan Rice, Lucas Paqueta and Scamacca in an attempt to win the game.
The lively Fabio Silva, Anderlecht's best player on the night narrowly missed the target when he sidefooted an effort just wide of the post with Areola left rooted to the spot. And that miss was to prove instrumental to the outcome of the game for just eight minutes later, West Ham grabbed the goal that won the game.
A superb team move saw the ball arrive at the feet of Brazilian international Paqueta on the edge of the box; he flicked the ball into the path of Scamacca who, with unerring accuracy, found the far corner with a low drive to score his fifth goal since moving to east London.
Down but not out, Anderlecht came back at West Ham in an attempt to regain parity and but for a sensational stop from Areola, they would have. There were just six minutes of normal time remaining when a cross from the right found Silva inside the six-yard box.
Climbing above the returning Ben Johnson, Silva's header appeared to be destined for the back of the net - until Areola thrust out a right hand and someone prevent the downward header from crossing the line.
It was, quite simply, one of the best saves any West Ham goalkeeper had even produced - and enough to see United over the line as Anderlecht failed to provide any threat thereafter.
While there were several good performances from West Ham players, one stood out particularly - that of midfielder Flynn Downes.
The youngster, who appeared to be channelling Mark Noble at times enjoyed a thoroughly productive evening at the heart of West Ham's midfielder and his efforts will no doubt have delighted David Moyes, who has been wary of breaking up the Rice/Soucek central midfield partnership due to a lack of competition.
Tonight, it seems he may have finally discovered it.
West Ham Utd: Areola, Coufal, Johnson, Dawson, Ogbonna, Emerson, Downes, Lanzini (Rice 69), Bowen (Fornals 86), Benrahma (Lucas Paquetá 69), Antonio (Scamacca 69)
Unused subs: Fabiański, Randolph, Cresswell, Kehrer, Zouma, Coventry, Souček, Scarles
Goals: Scamacca (79)
Booked: Lanzini (67), Ogbonna (73), Coufal (82), Downes (90+3)
RSC Anderlecht: Van Crombrugge, Debast, Hoedt, Delcroix (Moussa 87), Murillo, Ashimeru (Raman 65), Diawara (Esposito 87), Arnstad, Amuzu (Duranville 46), Verschaeren (Refaelov 80), Silva
Unused subs: Verbruggen, Coosemans, Vertonghen, Sadiki, Sardella, N’Diaye, Stroeykens, Stassin
Referee: Novak Simovic (Serbia)
Player of the Match: Flynn Downes
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