Chris Johnson led off the eighth inning with a homer to spoil an otherwise dominant start by Cliff Lee, Medlen allowed only two hits in eight innings and the Braves beat the Philadelphia Phillies 1-0 on Friday night.
Medlen and closer Craig Kimbrel combined on the shutout.
Johnson said beating Lee affirms Medlen's status as a starter who can lead a rotation.
"I feel like he can go toe to toe with anybody," Johnson said of Medlen. "If you can go toe to toe with that guy (Lee) over there, then you're an ace and he's our ace and he's proved it for a while now."
Medlen (15-12) strengthened his case to be the Braves' Game 1 starter in the NL division series next week. After not allowing a hit for 5 2-3 innings, he gave up two hits and two walks with seven strikeouts. He will carry a streak of five straight winning decisions into the postseason.
"I had to get ready for the big stage," Medlen said.
The Braves (95-65) remained tied with St. Louis, which beat Chicago 7-0, for the best record in the NL. The Braves won the regular-season series with the Cardinals and would win home-field advantage throughout the NL playoffs if they finish with the same record.
Medlen said the win was especially meaningful because of his respect for Lee and his history of struggles against the Phillies. He was 3-2 with a 5.17 ERA in 17 career games, including six starts, against the Phillies.
Medlen said the Phillies "absolutely owned me."
"They're just a team I've had so much trouble against," he said. "For me to have some success against them for even one game felt pretty awesome and I just want to take it to the playoffs."
The Braves' rotation is arranged for Medlen to start Game 1, but manager Fredi Gonzalez is waiting to make his plans official.
Kimbrel pitched a perfect ninth for his 50th save.
Johnson hit a 0-2 slider for the homer to left field. The homer, Johnson's 12th, snapped a streak of 16 consecutive batters retired by Lee, who allowed only three hits with no walks and 13 strikeouts in eight innings.
"Cliff was outstanding," Phillies manager Ryne Sandberg said. "Medlen was equally good."
Lee (14-8) completed a strong September finish despite the loss. He was 3-2 in five starts in which he had 54 strikeouts with only one walk.
"It basically came down to one pitch: 0-2 to Chris Johnson," Lee said. "I felt like I made a good pitch, slider down and in. I don't normally throw sliders to right-handers; I might have done that three times all year. Maybe four or five at the most. But I threw him one earlier today that he pulled way foul and I was trying to bury that one down and in. It was down and in. I think it was a ball, even. He put a good swing on it, hit a home run and that's the game.
"It's frustrating but you've got to give credit to Medlen. He shut us down."
Cesar Hernandez beat out a grounder to third base for an infield hit with two outs in the sixth, the first allowed by Medlen. Hernandez was thrown out by Evan Gattis trying to steal second base. Chase Utley, who had Philadelphia's second hit on a seventh-inning single, was thrown out on a double-play grounder by Carlos Ruiz, leaving Medlen as having faced only one batter above the minimum.
Medlen walked Ruiz to lead off the second before Domonic Brown hit into a double play.
Lee struck out the side in the fourth and fifth innings as part of a stretch in which he retired 16 consecutive batters.
Reed Johnson, making his first start since July 25, made a running catch of Jimmy Rollins' liner in left field in the first inning. Johnson missed 38 days with left Achilles tendinitis and had appeared only as a pinch hitter since coming off the disabled list on Sept. 10.
Dan Uggla struck out looking with runners on first and third to end the second inning. Uggla also took called third strikes from Lee in the fifth and eighth innings, giving the slumping second baseman a franchise-record 170 strikeouts, breaking his own mark. He had 168 strikeouts in 523 at-bats in 2012. The fourth-inning strikeout came in his 445th at-bat.
Uggla, Justin Upton (158) and B.J. Upton (151) rank third through fifth in the National League in strikeouts.
NOTES: The game lasted 2 hours, 7 minutes. ... Lee set his career high with 16 strikeouts in a 5-0 loss to the Braves on May 6, 2011. ... Braves C Brian McCann, who left Thursday night's game against the Phillies with an adductor strain, was held out and is not expected to start in the final two regular season games. Gonzalez said McCann is expected to be ready for the postseason. ... Gonzalez said he hopes RHP Jordan Walden (shoulder) can throw an inning this weekend. Walden has not pitched since allowing four hits and three runs in one inning against Washington on Sept. 17. ... Sandberg said RHP Ethan Martin "most likely" will start on Saturday against Braves LHP Mike Minor.