The teams have split back-to-back 14-inning contests, with the Mets avenging Friday night's 6-5 defeat by outlasting the Phillies 5-4 on Saturday thanks to David Wright's two-out go-ahead single.
The marathons have lasted a combined 10 hours and 55 minutes with 934 pitches thrown, leaving both bullpens taxed to a near-breaking point. Sixteen relievers - eight of them appearing in both games - have combined to throw 534 pitches in 32 innings.
"It's exhausting," manager Ryne Sandberg told the Phillies' official website. "It goes a long way with the pitching staff, that's for sure. But you know what, two days in a row both teams fought for 28 innings."
Saturday's loser Antonio Bastardo has allowed the lone run by Phillies relievers in 15 innings over the two contests, but the Mets (26-29) have conceded only three in 17 - and the 285 pitches logged by their bullpen are their most in consecutive games dating to at least 1988.
''The only thing we know is we won, don't ask me how,'' manager Terry Collins joked. ''There are a lot of tired bodies out there.''
Buddy Carlyle, called up from Triple-A after Friday's loss, got his first win since 2008 with three scoreless innings.
''Probably every pitcher is just as exhausted as I am,'' said Carlyle, who spent Saturday morning getting to Philadelphia from El Paso, Texas.
The Mets likely won't be able to call on Daisuke Matsuzaka and Jeurys Familia, and Josh Edgin and Scott Rice might be restricted to situational help. Left-hander Dana Eveland will be added to the roster before the game according to MLB.com.
For Philadelphia (24-29), Bastardo, Mike Adams, Jonathan Papelbon and Mario Hollands all have thrown at least one inning in both contests, and Jeff Manship - who strained his right quadriceps trying to beat out a chopper in the bottom of the 13th - is unavailable after striking out six in four hitless innings.
Bastardo has pitched four consecutive days, walking seven in three innings over that span, and likely would be only used as a last resort.
Niese (3-3, 2.74 ERA) has pitched at least six innings in seven of his 10 starts, but he has failed to do that in two of his last three. The left-hander struggled with his command Tuesday against Pittsburgh, walking four in 5 2-3 innings before New York pulled out a 4-2 win.
Niese did beat Hamels (1-3, 4.43) in a 6-1 victory April 29, holding the Phillies to one run in seven innings while Hamels was tagged for six in 4 2-3. On May 11, Hamels fanned 10 and allowed one run in seven innings and Niese yielded three in six of New York's 5-4, 11-inning victory.
Hamels lost to Colorado on Tuesday after giving up a tiebreaking homer in the seventh inning of a 6-2 defeat, and his 14 losses to the Mets are his most against any team. Wright is hitting .329 (23 for 70) with five homers and three doubles against the lefty, while David Murphy is 17 for 40 with a homer and four doubles.
This is the second straight year Philadelphia will deal with an overworked bullpen in a series - its relievers tossed 407 pitches Aug. 24 and 25 against Arizona, with 351 of them coming in a 12-7, 18-inning defeat. The Phillies won the following game 9-5.