In Game 1 of the Seattle Mariners-Boston Red Sox series at Fenway Park on Friday, Felix Hernandez allowed three runs in 5.2 innings -- the first time he'd allowed three runs in 18 starts.

In Game 2, Chris Young pitched just 3.2 innings.

In Game 3, Hisashi Iwakuma lasted just 2.1 innings, the shortest outing of his Mariners career.

What arguably has been the league's best trio of starting pitchers had a terrible weekend ... and yet the Mariners swept the Red Sox at Fenway for the first time in franchise history in a series of three games or longer.

Yes, you can credit the reeling Red Sox, now losers of eight straight, for helping out. You can credit the much-maligned Mariners offense that had a dramatic five-run ninth inning on Friday, a seven-run inning on Saturday and 13 hits on Sunday.

Mostly, you can credit the best bullpen in the league. Mariners relievers pitched 15.1 innings in the three games and allowed one run while punching out 21 Red Sox hitters as the Mariners rallied from deficits in all three games. Seattle's bullpen now owns a major league-best 2.38 ERA, which would be the lowest since the 1990 A's had a 2.35 mark. The average major league bullpen has allowed 3.86 runs per nine innings; the Mariners have allowed 2.63. Other bullpens may have better win-loss records -- Seattle's is 19-18, but you have to factor in the Mariners' lack of offensive punch -- but the pen has been a major reason the Mariners currently hold a tenuous grip on the second wild card over the Tigers.

A few keys to the pen's success: good health; expert handling by manager Lloyd McClendon and pitching coach Rick Waits; and a group that currently runs eight deep, most of whom can crank it up into the mid-90s -- the Mariners' average fastball velocity from their relievers is fourth highest in the majors. Leading the way there is converted starter Brandon Maurer, who bombed out of the rotation early in the year, but has averaged 96.1 mph with his fastball as a reliever while posting a 1.80 ERA.

I'm not a fan of having eight relievers on your roster, but these days, when complete games are few and far between (the Mariners have just one, from Roenis Elias), that depth has allowed McClendon to do some unusual things with his relievers. For starters, he's not afraid of a quick hook with his starters. Mariners starters have gone five or fewer innings in 40 games, the ninth-lowest figure in the majors -- even though Mariners starters have the third-best ERA in the majors. (The Braves have the fewest "quick hooks" with 22.) Obviously, Felix and Iwakuma usually go deep into the game, but knowing his offense doesn't score many runs, McClendon has been careful about not letting the game get away early when the other three starters are out there.

Despite the quick hooks -- which means using multiple relievers in the same game -- McClendon hasn't abused his relievers. According to Baseball-Reference.com, entering Sunday the Mariners had used the same reliever in back-to-back games just 64 times; only the Rangers, Blue Jays and Nationals had done so fewer times. And because he's rarely using his relievers in consecutive games, McClendon often lets his guys go more than one inning. Tom Wilhelmsen has 21 outings of more than one inning, fifth most among relievers, and has compiled a 2.03 ERA in those games, totaling 44.1 innings. Rookie Dominic Leone, who escaped a one-out, bases-loaded jam in the third inning on Sunday with an infield pop-out and strikeout, has 19 such appearances totaling 34.2 innings with an ERA under 2.00. With his philosophy of not using guys on back-to-back days, McClendon hasn't settled on just one eighth-inning guy, with Yoervis Medina and Danny Farquhar primarily sharing those duties.

McClendon has been conventional in his use of closer Fernando Rodney -- just two outings of more than one inning -- and lefties Charlie Furbush and Joe Beimel as LOOGYs, but that's not necessarily a bad thing. Rodney gets the glory with the saves and the arrows, but maybe that's a good thing since he gets to enter without runners on base; he's only fifth among the current Mariners relievers in OPS allowed (and just barely ahead of Farquhar).

Counting blown saves from the middle relievers, the Mariners have just 10 -- tied with the Royals for second fewest in the majors behind the Padres -- an impressive figure considering how many close games the Mariners play.

The Mariners are one game up on Detroit and you can point directly to the two bullpens as a reason why. Here are four other dominant bullpens that have helped contenders get where they are:

2. Kansas City Royals

The Royals don't have the Mariners' depth with a 3.40 ERA, but they do have the best late-inning trio in the majors in Kelvin Herrera (1.51 ERA), Wade Davis (0.80 ERA) and Greg Holland (1.79 ERA). Jason Frasor was acquired to add a strong fourth guy. The Royals haven't needed the depth -- their bullpen has pitched the second-fewest innings in the majors -- but it will be interesting to see if manager Ned Yost tries to get more out of this group down the stretch as the Royals battle the Tigers for the division crown.

3. Atlanta Braves

No surprise that the Braves would rank high with closer Craig Kimbrel once again crushing in the ninth inning. Like the Mariners, they don't usually have any margin for error considering their lack of runs. Manager Fredi Gonzalez has had to mix and match more than McClendon as David Carpenter and Luis Avilan haven't repeated their outstanding 2013 campaigns, but Jordan Walden and Anthony Varvaro have been solid in supporting roles and James Russell recently came over from the Cubs to give the Braves a lefty presence.

4. Los Angeles Angels

For the season, the Angels are just 14th in the majors with a 3.45 bullpen ERA (before their Sunday night game), but the bullpen you see now isn't the one that was there in April. General manager Jerry Dipoto has rebuilt much of the pen, with the likes of Huston Street and Jason Grilli joining rubber-armed Joe Smith, and since June 1 it has a 2.85 ERA and since July 1 a 2.32 ERA.

5. Baltimore Orioles

You can consider the A's here, except closer Sean Doolittle just went on the DL, or the Yankees, who have a strong back-end duo with Dellin Betances and David Robertson, but I'd go with the Orioles. Buck Showalter's pen didn't have a set closer back in April, but Zach Britton has run with the role (2.04 ERA, 27 saves in 30 chances) and the pen has picked up momentum as the season has progressed. It's no coincidence that the O's began pulling away in the AL East as the bullpen started dominating -- it has the fourth-best bullpen ERA in the majors since June 1.