Westerman switched positions after Kiwi Carlos Tuimavave went off injured in the first half at KCOM Stadium.
He went on to cross twice in the second period as Lee Radford’s side ensured they swiftly put their 62-16 Easter Monday debacle at leaders St Helens behind them.
This game proved scrappy, as is so often the case in the first after the double-header holiday weekend, but Hull always had that little bit more class to get home.
FC took the lead in the fourth minute when Albert Kelly, who excelled on his return to the stand-off role, stepped through and then did likewise to full-back Max Jowitt.
Marc Sneyd add the first of his seven goals - which included three penalties - but Jowitt quickly responded for Wakefield following a fine handling move.
Ryan Hampshire improved but Sneyd’s first penalty and then a try from Connor Wynne saw them back in front.
Kelly was beaten for pace, though, as Justin Horo won the race to a kick and the game was finely poised as the hosts led just 14-10 at the break.
However, Sneyd soon added his second penalty and - after a crucial Danny Houghton tackle denied Lee Kershaw - Westerman charged onto Kelly’s short pass for his first try.
He added another soon after meaning Jowitt’s second try in the 73rd minute was mere consolation, Sneyd slotting his final penalty with the last play of the game.
Hull FC: Wynne; Logan, Tuimavave, Connor, Griffin; Kelly, Sneyd; Taylor, Houghton, Paea, Manu, Hadley, Ellis. Substitutes: Westerman, Geen, Matongo, Fash.
Wakefield Trinity: Jowitt; Jones-Bishop, Lyne, Caton-Brown, Kershaw; Hampshire, Reynolds; Fifita, Wood, Hhirst, Kirmond, Horo, Crowther. Substitutes: Arona, King, Annakin, Pauli.
Referee: Liam Moore (Wigan)