The forward, who is on loan at the Hawthorns until the end of the season, poked home to give Darren Moore’s side a 68th-minute lead over the Lions.
And Kieran Gibbs’ confident finish eight minutes later sealed the points for the hosts, who recorded a fifth successive home victory, leaving them third in the Championship table – and just one point behind Leeds United and Middlesbrough at the summit.
Gayle was withdrawn by Moore with two minutes remaining, with Tosin Adarabioyo sent on in his place.
Dan Barlaser, meanwhile, made his first league start for Accrington Stanley, helping them to a 2-1 victory over AFC Wimbledon in League One.
The midfielder, 21, lined up for John Coleman’s men at the Wham Stadium as Billy Kee and Sean McConville strikes won it for the hosts, despite Scott Wagstaff’s consolation.
Barlaser was replaced by Seamus Conneely with quarter of an hour left, while Luke Charman wasn’t part of the Accies squad.
Jack Colback didn’t feature in Nottingham Forest’s 1-0 Championship win over Rotherham United on Saturday, and Henri Saivet started but was later substituted 77 minutes into Bursaspor’s goalless draw with Basaksehir.
In League Two, Josef Yarney completed 90 minutes as Morecambe earned a 2-1 win over Macclesfield Town, but Rolando Aarons’ Slovan Liberec were beaten 4-1 at Sparta Prague in the Czech First League.
Aarons started on the wing for the Modrobílí, but was replaced just after the hour.