The match was in the balance for long periods, and it took the 60th-minute dismissal of Vikings prop Ben Cross for the match to swing their way.
The game was finely balanced with the scores locked at 4-4 when a mass brawl erupted on the hour following a high tackle on St Helens captain Paul Wellens.
Referee James Child's response was to hand Cross a red card and send Widnes captain Jon Clarke to the sin bin and Saints took full advantage to seal victory with the aid of tries by Lee Gaskell and Francis Meli.
Widnes gave a debut to England forward Gareth Hock, who has joined them on loan from Wigan, while Saints were forced to cope without injured England hooker James Roby.
St Helens, who were looking to bounce back from a humiliating 40-4 home defeat by Huddersfield, also lost prop Josh Perry after only five minutes, following a crunching tackle by Hep Cahill, leaving Brown with the use of just three substitutes for the rest of the match.
Hooker Shaun Lunt scored twice as Huddersfield powered to their second win of the new season with a 34-6 victory over the London Broncos.
Lunt showed great feet to dodge with the ball between two defenders to reach the line on 19 minutes from Eorl Crabree's final pass. The former Castleford ace then charged down an attempted clearance and dashed 50 yards for a stunning solo effort on 69 minutes.
Lunt was also involved in the game's opening try, scored by prop Crabtree, playing a new loose forward role, after eight minutes. Danny Brough, who kicked five goals in last week's 40-4 win at St Helens, converted five out of Huddersfield's six tries.
Hull FC muscled up in defence to get the better of Bradford 28-12 at the KC Stadium and put their opening-night misery behind them.
FC were comprehensively beaten, 36-6, by Leeds in the first game of the 2013 season last week, producing a meek performance that belied their status as title dark-horses.
But they showed their mettle on Sunday, particularly in their own half, as they repelled a Bradford side on a high from their 40-point win over Wakefield last Sunday.