PHOENIX — J.D. Martinez tied another home run record with his 16th September homer on Wednesday. Just do not ask him if his remarkable production is surprising.

"If I say yes, it's like I don't think I can do it," Martinez said.

"If I say no, it's like I'm arrogant, cocky. It's one of those things where I go up there and expect to hit the ball hard. I just feel like right now I'm having success in being able to do what I want to do up there. I feel comfortable in the box and I'm getting the results."

Martinez's homer leading off the ninth inning -- his 45th of the season and 29th in 59 games in Arizona -- sparked a three-run rally in the Diamondbacks' 4-3 walkoff victory over the San Francisco Giants at Chase Field.

Martinez tied Ralph Kiner for the NL September record. Babe Ruth and Albert Belle hold the major league record with 17. The Diamondbacks have two more games this month, the first two games of a weekend series in Kansas City.

"It's cool," he said. "It's awesome. I'm flattered. It's humbling. Really, I don't get caught up in all that stuff."

First baseman Pablo Sandoval had two doubles and two RBIs for the Giants (62-97), who opened their season with a walk-off loss in Arizona. Sandoval is hitting .407 with four doubles and 10 RBIs in his last eight games.

Denard Span added three hits, finishing a homer short of the cycle, and scored two runs. The Giants need one victory in their final three games against the San Diego Padres to avoid the franchise's second 100-loss season.

Martinez is hitting .418 with seven doubles and 36 RBIs in September, breaking Luis Gonzalez's franchise record.

"What can you continue to say about J.D.?" Arizona manager Torey Lovullo said. "You're talking about historical records now. He’s locked in."

Giants closer Sam Dyson (3-3) took a 3-1 lead into the ninth inning after starter Jeff Samardzija gave up four hits and one run -- a Jake Lamb homer -- in six innings.

Lamb and Pollock followed Martinez's homer with singles, putting runners on first and third, before pinch-runner Kris Negron was thrown out at home on a grounder to second baseman Joe Panik.

After a double steal, pinch-hitter Jeremy Hazelbaker was intentionally walked. Shortstop Brandon Crawford threw late to the plate on John Ryan Murphy's grounder as the tying run scored, and David Peralta walked with the bases loaded to force in the game-winner in the Arizona's ninth walk-off win of the season.

"The way we came back in this game was unbelievable. We never give up, we always fight anybody," Peralta said.

Lamb's homer was his 29th as the Diamondbacks (92-68) won the fifth in their last seven.

J.J. Hoover (3-1) retired both men he faced in the ninth inning for the victory.

Samardzija, in line for his first victory since an Aug. 28 shutout at San Diego, struck out four and walked one. He finished the season with 205 strikeouts, second only to his career-high 214 set with the Chicago Cubs in 2013.

Span tripled on the fourth pitch of the game before Panik walked and Sandoval doubled to center field for a 1-0 lead. Panik scored on Crawford's groundout for the second run of the inning.

Span doubled to open the third and scored on Sandoval's second double to make it 3-0.

Arizona right-hander Braden Shipley gave up four hits and three runs in 3 1/3 innings. He struck out two and walked two. Shipley started when Zack Greinke was pushed back to Friday, the better to position him for a start in the wild-card game on Oct. 4.

NOTES: Giants RHP Matt Cain said his start at home Saturday will be the last of his career unless "something super crazy happens." Cain won 104 games and three World Series titles in 13 seasons with San Francisco after being the Giants' first-round pick in 2002. He will be 33 Sunday. ... Arizona LHP Robbie Ray will start the final regular-season game at Kansas City on Sunday, manager Torey Lovullo said, adding that the start would not preclude Ray from pitching in the NL wild-card game Wednesday behind starter RHP Zack Greinke if necessary. ... Arizona starters LHP Patrick Corbin and RHP Zack Godley will be used out of the bullpen this weekend, Lovullo said, with Corbin piggy-backing off Greinke on Friday and Godley piggy-backing off RHP Taijuan Walker on Saturday.