Daric Barton added a two-run single in the second as the A's knocked Clay Buchholz (15-7) out after only an inning-plus, his second-shortest outing as a starter and shortest in a non-injury situation.
Cahill (16-6), who began the year in the minors, became the first A's pitcher to reach 16 wins since Joe Blanton and Barry Zito in 2006. The only other pitcher in Oakland history to win more games without getting a victory in April was Vida Blue, who posted 17 wins in 1974.
This one hardly lived up to the billing of a pitchers' duel featuring 15-game winners and All-Star right-handers.
"Both are tops in baseball as far as ERA goes and performance," A's manager Bob Geren said beforehand.
Buchholz entered with a 2.25 ERA, to 2.72 for Cahill — Nos. 1 and 3 in the AL, respectively. Buchholz's went up to 2.53, while Cahill lowered his to 2.61.
The A's jumped on Buchholz in a hurry, starting with Coco Crisp's leadoff single in the first. Barton walked and Suzuki followed with his double.
Barton's big hit chased Buchholz after 39 pitches. His only shorter outing came in a one-inning stint at San Francisco on June 26. He left that one with a hyperextended left knee that he hurt running the bases.
Buchholz is winless in his last three outings following a four-start winning streak.
On the first play of the game, Crisp went over the center-field wall to steal a home run from Ryan Kalish.
Crisp also hit three singles against his former team and matched his career high with three stolen bases. He last stole three bags in a game on June 20, 2004, at Atlanta while with Cleveland.
This marks Boston's third trip to the Bay Area of the season — including one other visit to the Coliseum in July and a stop across the bay in San Francisco to play the Giants in June.
Cahill won for the fourth time in five starts, beating Boston for the first time in three career tries. He didn't allow an earned run for the sixth time in his last nine.
After a walk to No. 9 hitter Lars Anderson in the third, Cahill retired 10 of the next 11 batters. He allowed three hits, struck out four and walked two in seven innings.
Oakland's visiting clubhouse staff brought in extra lockers typically used by the NFL's Oakland Raiders in order to handle all the additional Red Sox. Their roster is at 34 after pitcher Matt Fox joined the team Friday. He was claimed off waivers from Minnesota on Thursday.
NOTES: The A's lead the season series 4-3. ... Red Sox LHP reliever Felix Doubront stayed back in Boston to undergo further tests on a strained muscle beneath his left collarbone. He isn't likely to rejoin the team until after its West Coast swing that also takes the Red Sox through Seattle. "We're just trying to be conscientious," manager Terry Francona said. "They'll probably send him to one more doctor, a neurologist." ... Boston SS Marco Scutaro had the night off. ... A's SS Kevin Kouzmanoff missed his fourth straight game and was still listed as day to day after experiencing lower back spasms Sunday at New York. ... Oakland LHP Josh Outman threw a bullpen session and RHP Joey Devine, who like Outman is coming back from Tommy John reconstructive elbow surgery, played catch on flat ground. ... Hall of Famer Rickey Henderson spent some of the game in the A's dugout.