Guardiola left City's joint all-time leading goal-scorer Sergio Aguero on the bench but his side still struck twice in a frantic five minutes at the Hawthorns which featured three goals in all.
Leroy Sane's stunning strike gave City a 10th-minute lead only for Jay Rodriguez to equalise soon afterwards.
But come the 15th minute, City were 2-1 up after Fernandinho let fly with a speculative shot that deflected off Gareth Barry and went in off the post.
City substitute Raheem Sterling gave the visitors a two-goal lead in the 64th minute only for the Baggies' to pull a goal back late on through Matt Phillips after a defensive blunder by Nicolas Otamendi.
"You cannot win all the time by four, five, six goals, that is unrealistic," said Guardiola, whose side have won 28 points from a possible 30 in their opening 10 league games this season.
"It's important when you make a good performance you win comfortably and when you don't play at the high level you're able to win."
Second-placed Manchester United and Tottenham Hotspur started the day level on points but Jose Mourinho's men edged ahead after substitute Anthony Martial's goal nine minutes from time gave them a 1-0 win over a Spurs side missing injured England striker Harry Kane.