Tony Vitello explains his decision to have Matt Gage face Ketel Marte in the game's deciding at-bat.

The San Francisco Giants suffered a heartbreaking loss to the Arizona Diamondbacks. A ninth-inning lead evaporated as Ketel Marte blasted a Matt Gage slider into the seats beyond Arizona’s bullpen to walk off the Giants, 5-3, at Chase Field.

The fateful decision before the walk-off blast was manager Tony Vitello’s decision to bring in Gage. The Giants manager accepted the blame for the loss in his postgame presser.

“[Caleb] Kilian had 25 pitches, went with a fresh arm and a different look,” said Vitello on NBC Sports Bay Area’s postgame coverage. “Made the wrong decision and cost us the game.”

Diamondbacks’ Late Rallies Force Tony Vitello to Make ‘Wrong’ Decision

The Giants carried a 3-1 lead into the ninth. Back-to-back home runs from Rafael Devers and Willy Adames, followed by a Daniel Susac RBI double, in the second inning put San Francisco up for the whole game.

But the Diamondbacks continued to mount rallies late in the game, loading the bases in both the seventh and eighth innings before Giants relievers escaped with inning-ending double plays. Caleb Killian induced the second one off the bat of Nolan Arenado to finish the eighth.

Vitello sent out closer Kilian for the ninth to complete a five-out save. Ildemaro Vargas singled to lead off the inning, then advanced to second on defensive indifference. Adrian Del Castillo drove Vargas home on his own single to cut the lead in half.

Then Susac committed catcher’s interference, allowing Ryan Waldschmidt to reach. That brought Marte to the plate in what was going to be the game’s deciding at-bat. With Kilian on his second inning of the evening, and 25 pitches, Vitello brought in Gage to get the final out and preserve a 3-2 lead.

“Gage has as good a number as anybody on our team. He’s gotten it done more times than not.”

While Gage has a 1.40 ERA and a save in 23 appearances, further inspection of his playing record doesn’t suggest a shutdown reliever who should be getting this opportunity.

Entering the game, the left-hander has a walk rate of 14.1% compared to a 16.7% strikeout rate. His 4.14 FIP and 5.00 xFIP suggest a future regression candidate, as his .189 BABIP and 87.4% strand rate will regress toward league averages.

Additionally, Gage’s ability to get the job done isn’t as strong as the Giants manager said. He carries five shutdowns, a relief appearance with +6% win probability added, compared to three meltdowns.

Questionable Move by Tony Vitello Backfires

Despite the left-hander carrying a 1.40 ERA on the season, despite questionable peripherals, it’s considered a questionable move to turn Marte to the right side in a key situation. Even though his numbers aren’t to their usual standard, hitting .255 with a .603 OPS, the switch-hitter has more power from the right side of the plate.

Per Statcast’s bat tracking metrics, Marte sees a 5 MPH jump in swing speed when batting right-handed (77.4) vs. left-handed (72.7). The All-Star second baseman connected on a Gage slider just below the knees to end the game right there.

The latest loss by the Giants not only results in a series loss but continues a slide for the first-year manager. San Francisco is now 20-29 on the season, only a game ahead of the Colorado Rockies for the worst record in the National League.