How Veteran Reliever's Ugly 2025 Was Bad Omen for D-backs Bullpen

It was the beginning of the end for this Arizona Diamondbacks left-hander.

Apr 11, 2025; Phoenix, Arizona, USA; Arizona Diamondbacks pitcher Joe Mantiply (35) throws in the ninth inning against the Milwaukee Brewers at Chase Field. Mandatory Credit: Matt Kartozian-Imagn Images | Matt Kartozian-Imagn Images

The Arizona Diamondbacks' 2025 season was anything but a smooth ride, particularly with regard to a battered and underperforming pitching staff.

It took the D-backs more than their fair share of pitchers to grind their way through the 162-game marathon season, and Arizona Diamondbacks On SI continues its player-by-player review of everyone who contributed to the ultimate 80-82 2025 season.

For the purpose of this article, we'll be using aWAR, the average of Baseball-Reference and FanGraphs WAR.

The D-backs' bullpen was a source of frustration, heartbreak and instability in 2025. And the trouble began early.

Perhaps one of the early warning signs of how 2025 would eventually fall was the rapid, severe decline of veteran left-hand reliever Joe Mantiply.

It was a handful of particularly bad outings that eventually ended his tenure in the desert.

Arizona Diamondbacks Player Review: Joe Mantiply

Joe Mantiply 2025 and career statistics. | Alex D'Agostino

Mantiply had been a valuable, reliable reliever in Arizona's bullpen over the past four seasons, including accounting for the D-backs' lone All-Star representative in the 2022 season.

Unfortunately, he struggled greatly to open 2025, and never truly recovered from a lopsided start.

In just his second appearance of the year, Mantiply allowed three runs without recording an out. That would end up being a bad omen. He put together two more scoreless outings, but then hit an even rougher stretch to close out his short MLB season.

Over his final six appearances (8.1 innings), Mantiply gave up 14 earned runs. Four of those six outings were multi-run affairs.

The one that stood out the most came on April 18. Arizona had just managed to complete what was shaping up to be an absolutely stunning comeback victory over the Chicago Cubs, rallying from down 7-1 with a 10-run eighth inning.

But Mantiply (along with right-hander Bryce Jarvis) would combine to surrender the lead the very next half-inning. Mantiply himself was responsible for six hits (including two homers) and three earned runs, as the D-backs went on to lose 13-11 in heartbreaking fashion.

Related Content: Ranking 3 Most Painful D-backs Losses of 2025

That outing was the beginning of the end of Mantiply's tenure with Arizona, and a severe warning sign of the bullpen struggles to come. It was around that time that the D-backs' bullpen began to devolve into instability, as A.J. Puk went on the IL a day later. It only got uglier from there.

Mantiply was optioned to Triple-A, then came back and delivered two more poor outings. He was designated for assignment and eventually released on June 1.

He signed a minor league deal with the Toronto Blue Jays, but never got back to the MLB level, and has since elected free agency.

Mantiply has always been a pitcher whose peripherals were more positive than his overall results. He's been challenged by some of the toughest hitters in baseball, and was even used as an opener in the 2023 Postseason.

Unfortunately, his numbers in 2025 necessitated the harsh reality of an eventual departure. Mantiply will be remembered as a valuable D-back, but his time in Arizona has come to an end.