Baker did not have closer Aroldis Chapman, nor setup man Jonathan Broxton, at his disposal. Chapman had worked five of the previous six days and the last two in a row.
"We had to call on the other guys," Baker said.
The Reds were leading 3-2 in the eighth when reliever Sean Marshall gave up a one-out single to Domonic Brown. Looking for a double play, Sam LeCure got two balls hit on the ground, but both went for singles by Mayberry and Erik Kratz to load the bases. The tying run then scored on Jimmy Rollins' sacrifice to short left field, with Brown beating Ryan Ludwick's throw home.
It marked the first time all season that Johnny Cueto was the victim of a blown save, which prevented him from being first in the Majors to 17 wins.
Freshly recalled rookie reliever J.J. Hoover worked out of a bases-loaded, one-out jam in the ninth-inning by getting a double play. Hoover found himself with runners on second and third with one out in the 10th and dodged the danger again when he got Juan Pierre to end the inning with a pop out.
Alfredo Simon took over for the Reds in the 11th inning and Kevin Frandsen led off with a single to right field. Chase Utley was next and he laced a double down the right-field line. Ryan Howard was intentionally walked to load the bases with no outs. With one out, Mayberry grounded a single through the left side to end it.
"It's hard to keep playing Houdini all the time," Baker said. "The [Phillies] didn't quit. They kept fighting and battling."
The Reds still haven't won at series at Citizens Bank Park since 2006. They haven't won a four-game series in Philadelphia since 1997, at Veterans Stadium.
"We could have got that last one, but that's baseball," said third baseman Todd Frazier, who drove in all three Reds runs. "Taking a split in Philly is really good. We're trying to win every series, but we'll take two out of four."
Including Game 3 of the 2010 National League Division Series, when he put the Reds away for the winter with a five-hit shutout, Hamels entered the night 8-0 with a 1.26 ERA in 10 lifetime starts vs. Cincinnati.
In a 34-pitch top of the first, as heavy showers started at first pitch and made the mound slick for Hamels, two singles and a four-pitch walk loaded the bases with one out. It wasn't quite a fruitful rally, as Frazier's RBI groundout to third base scored Zack Cozart for a 1-0 lead. Hamels went on to retire 10 in a row and 14 of 16.
Following two singles off Hamels to begin the sixth, Frazier lifted a two-run double off of the center-field wall. On the carom, the ball went between Laynce Nix's legs for an error that put Frazier on third base, but the Reds failed to get Frazier home.
"He's a great pitcher. To get three off him is really good," Frazier said.
Cueto also labored as he lasted five-plus innings, the first time since July 6 that he didn't complete six innings. He still leads the NL with a 2.47 ERA after he was charged with two runs on five hits, with three walks and four strikeouts.
"Hamels came in and did his job. I did my job," Cueto said through an interpreter. "It's the way it goes. He's a great pitcher. You have to give it to him."
Cueto, who escaped jams in lengthy second and third innings that ran up his pitch count, began the sixth by walking Howard and had runners on second and third base when Brown hit a double to the left-field wall. Jose Arredondo took over and Philadelphia notched back-to-back sacrifice flies by Nix and Kratz to make it a 3-2 game.
"I feel like I've been in a fight and I lost," Phillies manager Charlie Manuel said. "I feel drained. Really, I kept waiting for somebody to come home."
That wasn't to be for the Reds, who did not get hit over the final five innings. For the two teams, it was their third straight one-run game. For the first-place Reds, who hold a seven-game lead over the Cardinals, it was good test before the stretch run and postseason.
"They had a packed house here all the time and a lot of noise, a lot of energy and a lot of excitement," Baker said. "That was as close to playoff action as we could get to prepare us for the Cardinals series [this weekend] that will be the same."