Matt Chapman capped a fourth-run ninth inning with a three-run home run Thursday night, allowing the host Oakland Athletics to rally for a 5-4, walk-off victory over the Tampa Bay Rays in the opener of a four-game series.

The improbable finish came after the Rays had taken advantage of Blake Treinen's wildness to score three times in the top of the ninth to go up 4-1.

Rays closer Diego Castillo (1-5) walked two of the first three batters he faced in the last of the ninth, but got within one out of his eighth save before Marcus Semien singled in a run to get Oakland within 4-2.

Two pitches later, Chapman bombed a Castillo slider well into the seats in left-center field, a three-run shot that gave the A's their fifth walk-off win of the season. The homer was Chapman's 17th of the year.

The teams entered the ninth in a 1-1 tie that was the product of dueling solo home runs by Tampa Bay's Tommy Pham and Oakland's Jurickson Profar, and impressive starting pitching by the Rays' Charlie Morton and the A's Frankie Montas.

Treinen took over to start the ninth and immediately walked Pham and Brandon Lowe to set the stage for the Rays' scoring. Avisail Garcia followed with a single that plated Pham with the go-ahead run, after which Ji-Man Choi singled in Lowe to make it 3-1.

Ryan Buchter replaced Treinen, who didn't record an out, and the Rays completed their three-run inning when Willy Adames squeezed home Garcia.

Lou Trivino (3-5), who got the final out of the top of the ninth, was credited with the win. Neither starting pitcher got a decision.

Morton, who beat the A's 6-2 last week, took a one-hit shutout one out into the fifth before serving up Profar's 10th home run of the season. The veteran was pulled one out into the seventh inning, charged with one run on four hits. He walked two and struck out six.

The A's 1-0 lead was short-lived. Shut out on three hits by Montas for 5 1/3 innings, the Rays got even on Pham's 11th homer of the season.

Montas went on to work eight full innings, allowing one run and four hits. He struck out nine and did not walk a batter.

Chapman finished with two hits for the A's.

--Field Level Media