Last season the Baggies held Spurs to a 1-1 draw at White Hart Lane, which significantly affected their late title challenge.
Tottenham's Jan Vertonghen in action with West Brom's Salomon Rondon
Merson does not expect a repeat, with Tottenham in excellent form, putting together a winning streak since losing to Manchester United in early December.
He said: "It will be a hard game but I expect Spurs to win. Dele Alli is in great form and I was very impressed with the way they beat Chelsea. Spurs had to win and they played well.
"West Brom could easily have got draws at Arsenal and Chelsea so it will be difficult for Spurs, but I think they will win."
Merson is expecting the same scoreline as Tottenham's win over Chelsea, a 2-0 win for the hosts.
Tottenham's Dele Alli scores their second goal
The victory over Chelsea saw them rise to third in the Premier League table, above rivals Arsenal, but all that hard work will be undone if they slip up in Saturday's early kick-off.
West Brom have had a good start to the season but their progress has been halted by a tough run of fixtures over the past month.
They have rallied over the past two league games, beating Hull and Southampton, and currently sit in eighth position in the league, 13 points below Tottenham.