George Springer hit a home run to lead off the first inning for Toronto. It was his 55th career leadoff homer and moved him into second place on the all-time list behind Rickey Henderson (81).
Toronto took the rubber match of the three-game series after dropping the opener on Friday. Oakland has lost 10 of 11 games.
Tony Kemp hit a home run for Oakland, which was out-hit 11-3.
Kikuchi (7-2) allowed one run, two hits and two walks while striking out eight in seven innings.
Oakland right-hander Luis Medina (1-7) allowed four runs (three earned), four hits and seven walks in five innings. He struck out four.
Springer hit his 11th homer of the season to open the first. Whit Merrifield walked and scored on center fielder Esteury Ruiz's error on Vladimir Guerrero Jr.'s single.
Toronto scored once in the second. Santiago Espinal and Kevin Kiermaier walked, Tyler Heineman bunted for a single. A run scored when Springer grounded into a double play.
A wild pitch scored a Toronto run in the third. It came after the bases were loaded on walks to Chapman and Espinal and a Biggio single.
The Athletics had their first baserunner when Carlos Perez doubled to right with one out in the fourth
Kemp led off the sixth with his third home run of the season, a drive to right.
Ruiz misplayed Kiermaier's drive to center against Ken Waldichuk into a triple to lead off the Toronto sixth. Springer hit a sacrifice fly.
Bo Bichette extended his hit streak to 11 games when his infield single led off the home seventh. Guerrero doubled. Espinal followed with a two-run double to center that eluded Ruiz for a 7-1 advantage.
Heineman left the game in the home eighth when he injured his back during his at-bat. Fellow catcher Danny Jansen took over the plate and walked. Springer singled and Bichette hit an RBI single. Another run scored on Guerrero's fielder's choice grounder against Yacksel Rios. Chapman walked and Biggio hit his seventh homer of the season.
--Field Level Media