Mayberry hit an RBI single with two outs in the 10th inning, lifting Philadelphia over the Chicago White Sox 4-3 on Sunday.
The Phillies have won nine of 13 and stand 6½ games behind NL East-leading Atlanta.
"It's definitely exciting to pull that one out," Mayberry said. "It definitely gives us momentum and being able to carry momentum into the All-Star break and second half."
Ramon Troncoso relieved and struck out Young. But Mayberry lined Troncoso's first pitch up the middle for the winning run.
"I think this sets us up," Phillies manager Charlie Manuel said. "We've got to get going, we've got to get some wins."
Antonio Bastardo (3-2) pitched a scoreless 10th to earn the victory.
All three games in the series went extra innings. The teams played a total of 34 innings over 11 hours, 12 minutes.
The White Sox scored a run in the ninth off Jonathan Papelbon, who blew his fifth save in 25 chances.
Brown, picked for his first All-Star team, drove in a pair of runs and upped his team-leading total to 67 RBIs entering the break to help the Phillies reach .500 for the first time since June 7.
"The bottom line is if you don't finish in first place or get in the playoffs, you haven't done anything," Manuel said.
Cole Hamels was poised for his third straight win after a poor start to the season prior to Papelbon's blown save.
The left-hander has a 1.57 ERA in his last three starts. He allowed two runs and eight hits while striking out seven and walking none in eight innings. The three-time All-Star enters the break with a 4-11 record, but he is encouraged by his performance of late.
"To put the team in situations where we win, that's ultimately the big idea," Hamels said. "(Earlier in the season) I was a little wild and not able to pitch deep in ballgames."
Alejandro De Aza homered for Chicago, which enters the All-Star break having lost seven of its last 10 and 31 of 44.
"The record stands for itself," manager Robin Ventura said of the White Sox, who dropped to 18 games below .500. "We'll just go home, try to clear our minds and get ready to go in the second half."
Brown's two-run double in the first off Jose Quintana gave the Phillies a 2-0 lead. Philadelphia added a run in the fourth on Hamels' RBI single, the first of his two hits.
The White Sox scored in the seventh on Jeff Keppinger's RBI single.
De Aza hit a solo homer in the eighth.
Papelbon was booed loudly as he walked back to the dugout after the inning ended.
"He might be getting a little spent this time of year," Manuel said. "The break is going to be real good for him."
Quintana allowed three runs on five hits in six innings. It was the ninth straight start without a loss for Quintana, who has just one win during that span.
The Phillies have won five of their last six series. ... Phegley exited in the bottom of the ninth with an injury to his right index finger after taking a foul ball off the hand. X-rays were negative. ... The Phillies put OF Ben Revere on the 15-day disabled list with a broken right foot and activated C Erik Kratz. Revere, who was injured fouling a ball off his foot on Saturday, will have further tests on Monday to determine the extent of his absence. ... White Sox INF Gordon Beckham, who is batting .378 in his last 19 games, didn't play after getting a bruised thigh in the second game of Saturday's doubleheader.