OAKLAND, Calif. -- Seattle Mariners right-hander Felix Hernandez insisted he had the worst pregame bullpen session of his career Monday night.

However, if there is something the veteran has learned in his 375-start career, nothing counts until the umpires show up.

Hernandez passed the 2,500-inning milestone with six innings of two-hit ball, pitching the Mariners to a 7-1 victory over the Oakland Athletics in the opener of a three-game series.

Mitch Haniger, Mike Zunino and Yonder Alonso, all of whom have ties to the San Francisco Bay Area, combined for four home runs in support of Hernandez, helping the Mariners beat the A's for a seventh straight time.

"You've got to go out there and compete. That's my mantra," Hernandez said. "I was just trying to get through five or six innings. Mike's homer (a three-run shot in the second inning) helped."

Marcus Semien accounted for the only run off Hernandez with a solo homer in the sixth inning for the A's, who saw a season-best, seven-game winning streak come to an end.

"He kept the ball down, which he does," A's manager Bob Melvin said of Hernandez. "And when he keeps the ball down, he keeps (the contact) on the ground."

Hernandez (6-5) allowed a first-inning single to Matt Joyce and the sixth-inning homer to Semien in a 70-pitch effort that produced his first win since July 15.

Given the report he got from the bullpen before the game, Mariners manager Scott Servais was thrilled he got the 70 from his ace.

"I was told, 'He's got nothing. It's not going to be good,'" Servais said. "It goes to show what kind of talent he has."

Hernandez reached 2,500 innings when he struck out Jed Lowrie for the second out of the fourth inning.

The 31-year-old became just the second active pitcher to complete 2,500 innings for the same team, joining Justin Verlander in that distinction.

"It means a lot," Hernandez said of achieving the feat with one team. "I am going to be loyal to this team. I am going to help this team make the playoffs. It's not going to happen this year, but we'll try again next year."

Verlander accomplished the feat for the Detroit Tigers before getting dealt to the Houston Astros this season.

In recording his 160th career win, Hernandez ran his record against the A's to 25-9, including 13-3 at the Oakland Coliseum.

He walked two and struck out two.

Zunino, whose dad, Greg, played baseball at nearby Cal, gave his batterymate all the offensive support he would need with the three-run homer off A's starter Daniel Gossett (4-10).

Zunino's 24th homer, which followed a Kyle Seager walk and one-out single by Alonso, gave Seattle an early 3-0 lead.

Haniger, a product of Archbishop Mitty High in San Jose, added to the runaway win with a solo home run in the third inning and two-run shot in the fifth.

The two-homer game was the first of his two-year career and ran his 2017 total to 16.

"It's good to see those guys finish strong," Servais said of Zunino and Haniger, a pair of 26-year-olds. "They're playing with a lot of confidence right now. They're a big part of this organization."

Alonso's homer, a solo shot, came in the fourth inning. Traded to the Mariners from the A's for Boog Powell last month, Alonso had two hits in the game, including the homer, his 26th of the season.

The Mariners totaled only seven hits, five of which went for extra bases.

Semien's homer was his eighth of the season.

The A's, who had won their previous eight home games, finished with just four hits.

Mariners left-hander Andrew Albers, pitching out of the bullpen for just the third time this season, complemented Hernandez with three innings of two-hit relief for his first career save.

Gossett was pulled one out into the fifth inning with the A's trailing 7-0. Four of the six hits he allowed were homers. He walked two and struck out four.

"Poor pitching. No way to get around it. Let the team down," Gossett said. "I couldn't find that good breaking ball. Everything was (middle of the plate) or (in the dirt)."

The four home runs equaled the total number that Gossett had given up in his four previous September starts.

NOTES: Mariners 1B Yonder Alonso's home run was his 16th of the season at the Oakland Coliseum this year. Only Athletics LF Khris Davis (25) has more. ... A's manager Bob Melvin announced before the game that slugging 1B Matt Olson (strained hamstring) will likely miss the entire Seattle series and might be done for season. Olson was injured stretching for a throw during the Athletics' Sunday win over Texas. ... Likewise, Mariners manager Scott Servais ruled SS Jean Segura (sprained middle finger) out for the series, with the possibility of returning for the final regular-season series against the Los Angeles Angels. ... For the second game in a row, A's C Bruce Maxwell took a knee during the playing of the national anthem, which was performed by the Oakland Unified School District Honor Band. Members of the band knelt in unison during the performance.