|Widnes Vikings (4) 8|
|Tries: Ah Van, Thompson|
|St Helens (12) 21|
|Tries: Swift 2, Fleming, Vea Goals: Walsh 2 Drop goal: Walsh|
Widnes finished with 11 men as Kevin Brown and Patrick Ah Van were sent off for their involvement in a fight late on in their home defeat by St Helens.
Fourth-placed Saints' Joe Greenwood was sin-binned for his role in the melee.
Two first-half tries from Adam Swift put St Helens 12-4 up at the break, with Ah Van responding for Widnes.
Saints' Matty Fleming and Widnes' Corey Thompson traded tries and Atelea Vea added a further score for the visitors after the dismissals.
Victory is Saints' 10th in 11 games and keeps alive their hopes of finishing third in the table. However, their prospects of a top-two finish and a home play-off semi-final are remote given their points difference is vastly inferior to Warrington's.
Widnes' chances of a a sixth-placed finish had been dashed even before their defeat after Castleford beat Catalans Dragons on Saturday.
An injury-hit Saints side lost both Swift and Greg Richard to concussion but still managed to stay on top, with Fleming going over and Walsh adding a drop-goal with five minutes remaining.
Ah Van, despite his sending-off, was named Widnes' man of the match after leaving the field.
Widnes boss Denis Betts: "I didn't see it (the fight). It was pushing and pushing but I didn't see it.
"I came down the stairs and I see Kev walking off and then Pat walking a minute later.
"I can make something up for you but it was handbags at dawn, frustration. It looked a frustrating game."
St Helens assistant coach Jamahl Lolesi: "I couldn't see what happened but from what I've been told by the lads it was just us reacting - we didn't go looking for a fight.
"Overall I am delighted and very happy with the defensive effort.
"Everyone knows Widnes can attack. In Kev Brown they have a great player who can do some special things, so for us to only concede one try and another from a kick is a pleasing effort.
"If you had given us 10 wins and one loss then we would have bitten your hand off."
Widnes Vikings: Hanbury; Thompson, Dean, Runciman, Ah Van; Mellor, Brown; Burke, White, Buchanan, Whitley, Houston, Leuluai.
Replacements: J Chapelhow, Manuokafoa, Heremaia, Farrell.
St Helens: McDonnell; Owens, Peyroux, Fleming, Swift; Turner, Walsh; Amor, Roby, Richards, Wilkin, Greenwood, McCarthy-Scarsbrook.
Replacements: Walmsley, Vea, Thompson, Knowles.
Referee: James Child