Only two National League relievers since the end of 1983 have thrown six or more innings of one-hit ball - and arguably, neither were "really" relievers. One was the renowned "power outage" game in San Diego back in 2001, when a transformer blew during a Curt Schilling start after two innings, causing play to be suspended for the night. The next day, Randy Johnson took the mound and threw seven shutout innings, allowing one hit, for the most bizarre one-hitter ever in franchise history. Oh, and Johnson struck out sixteen: no other reliever in the live-ball era had ever K'd more than 13, and even that was more than 50 years ago now. So, not a genuine relief outing.
The other was on May 4, 2002, and was somewhat more legitimate. Jason Schmidt started for the Giants against the Reds in San Francisco, but could only get two outs in the first inning - seems he was coming off a groin injury. He was replaced by Ryan Jensen, who then shut the Reds down on one hit until the end of the seventh inning, throwing 93 pitches, with one walk. There's a "however" here too, in that Jensen was almost exclusively a starter - 30 of 32 games that season - whose scheduled start a couple of days earlier just happened to fall on an off-day, and had been skipped by the Giants. Collmenter has done nothing but relieve this season.
Outside of the Big Unit's outing, only two relievers in Diamondbacks' history have had five-inning appearances. Josh Collmenter this season is both of them. He worked five innings in the opening series against the Cardinals, picking up the W for his one-run effort, on four hits and two walks. But this afternoon was even better. Admittedly, the Marlins offense is one of the most historically awful of all-time - their current wRC+ of 69 is the worst in over 90 years - but they are still, at least in name, a major-league outfit. The fact that the game was scoreless, meaning the go-ahead run was at the plate every single time he took the mound, made it even more impressive.
So it's not the first time Collmenter has been an absolute life-saver. Just earlier this month, in St. Louis, he threw four scoreless innings against the Cardinals, picking up the victory as we won in 14 innings. That got him a Win Probability of over +50%, only the fourth time ever an Arizona bullpen arm has reached that level of WP. It looks like his figure for the game today will be over +40%, for the second time this season, putting him alongside Jose Valverde and Byung-Hyun Kim as Arizona relievers with more than one appearance of that importance. His 2013 figure of +144% puts him in the top ten NL relievers for that statistic.
That's in part because Collmenter has been particularly good when the game is on the line, with the scores tied. Including today, he has now kept opposing hitters there to a .172 average, allowed just one extra-base hit (a double) in 58 at-bats, and owns a K:BB ratio in such situations of 18:4. Frankly, I have much more current confidence in Josh's ability to put up a zero when it counts, than I do in Heath Bell. But he has also been a massive innings eater: Collmenter is now on pace for 91.5 innings in relief this year, a figure reached only once by a "pure" reliever in this league since 2007 (Matt Belisle threw 92 for the 2010 Rockies).
Today was a perfect example why Collmenter is, perhaps, the unsung hero of the team thus far. Trevor Cahill was unable to complete the first at-bat in the second inning after being hit on the hip by a line-drive: even with an off-day tomorrow, it would have been a fraught process to piece together eight innings from "normal" relievers, used to one-inning stints. But Collmenter took care of almost all the heavy lifting, and produced arguably the best relief performance in team history. Indeed, had it been a start, it would have resulted in a Game Score of 76 - tied for third-best of the year by a Diamondback [trailing only Corbin and McCarthy's complete games].
Enjoy your off-day, Josh: for you have certainly earned it.