Robinson Cano tripled to start a four-run fourth and Posada rounded the bases twice on his solo shot in the sixth, which was changed to a home run after umpires watched the video replay.
"They probably didn't see me run them the first time, so I did it again," he said.
Nick Swisher had an RBI single for the Yankees, who have won four straight and 14 of 18 overall. By taking the first two games against Milwaukee in an interleague matchup of division leaders, New York clinched its sixth consecutive series victory since getting swept at home by Boston from June 7-9.
The AL East leaders announced good news on three injured All-Stars, too.
Derek Jeter could rejoin the team next week in Cleveland, ready to resume his pursuit of 3,000 hits. Phil Hughes was sharp in a rehab start for Double-A Trenton and could be back in the rotation real soon. And fellow right-hander Bartolo Colon is lined up to pitch Saturday against the Mets if all goes well this week.
"The healthier we are, the better we're going to be. There's no question about that," Martin said.
Without them, the Yankees are doing just fine. They improved to 11-3 since Jeter went on the 15-day disabled list with a strained right calf -- he was eligible to come off Wednesday, but wasn't ready yet.
That was it for Burnett (8-6), who left to a standing ovation after losing three of his previous four starts. Helped by three double plays, he gave up two runs and seven hits while walking two and striking out four.
"It's all mental, man. It's sad but true," Burnett said. "It's believing in all my pitches."
Mariano Rivera got three outs for his 21st save in 24 chances.
New York goes for a sweep Thursday afternoon, with CC Sabathia pitching against the Brewers for the first time since carrying them to the 2008 playoffs.
Ryan Braun had three singles and an RBI for the Brewers, extending his career-best hitting streak to 19 games. Shaun Marcum (7-3) allowed four runs and five hits in five innings after being limited to four innings over his previous two starts by a strained left hip flexor.
Milwaukee dropped to 15-26 on the road, the worst record among winning teams in the majors. By comparison, the NL Central leaders are 29-11 at home.
"I'm hoping this team is what we all feel it is, and that's a team that can play with anybody," Brewers manager Ron Roenicke said. "When we're playing our good game, I feel good about us."
Marcum kept the Yankees off the scoreboard until giving up four consecutive rockets to begin the fourth.
Nyjer Morgan crashed hard into the center-field fence while chasing Cano's triple, but seemed to be fine and stayed in the game. Swisher lined a single and Posada ripped a long single off the base of the right-field wall.
Martin lifted a low 0-2 pitch into the left-field seats for his first extra-base hit in 68 at-bats since his last homer on May 24. That was the longest drought of his career, the Yankees said, according to information provided by the Elias Sports Bureau.
"It felt like it had been a while," Martin said. "Obviously, I want to do well offensively, but I kind of don't really think about it when we're winning so many games. It's definitely nice to join the party a little bit."
Posada sent a liner to right in the sixth that barely cleared the wall, caroming off a ledge behind the fence and then a fan before bounding back toward the field.
Umpires originally ruled the ball in play and called Posada out when the Brewers tagged him between first and second. Posada pointed toward the right-field stands and then rounded the bases as the umpires huddled.
They told him to wait at first base while they went inside for a look at the replay, and he trotted around again when they came out and correctly signaled home run.
Yankees center fielder Curtis Granderson made a terrific, over-the-shoulder catch to start a double play in the second, with Hart doubled off first base.
Milwaukee loaded the bases in the sixth, but Burnett retired Prince Fielder on an RBI groundout and then induced a grounder from Hart to end the inning.
"A.J. and Russ, those guys stole the show," Swisher said. "I couldn't be happier for them."
After the game, the Yankees reacquired RHP Sergio Mitre from Milwaukee for cash. To make room on the roster, RHP Buddy Carlyle was designated for assignment. ... Slumping 3B Casey McGehee was dropped from fifth to seventh in the Milwaukee lineup, with Hart batting fifth. ... New York is 10-4 in interleague play.