Braun hit a three-run double and scored on Johan Santana's throwing error, sending the Brewers to a 6-3 victory on Tuesday night that extended New York's losing streak to a season-high five games.
Afterward, the injury-depleted Mets held a closed-door meeting that lasted almost 30 minutes. Manager Jerry Manuel said he was the only speaker.
"We just had a little family talk -- a little private family discussion," Manuel explained. "Just to get things in order, a lot of things."
Fielder added a 452-foot solo homer and fill-in starter Mike Burns earned his first major league win for the NL Central leaders, who have won four of five. The Brewers have a two-game lead over St. Louis despite a 12-15 mark in June.
"It couldn't get much better," Braun said. "We have a tough schedule up until the All-Star break. We've got these guys one more day, go to Chicago and then we've got the Dodgers and Cardinals.
"It's definitely not going to be easy and I think where we finish out the rest of the first half is probably going to be pretty indicative of how the rest of our season will go."
The Mets hope their fortunes change before they fall out of postseason contention. They went 9-18 in June, their worst month in nearly six years. At 37-39, the third-place Mets are three games behind first-place Philadelphia in the NL East and only a game in front of Atlanta.
They head into July still missing injured stars Carlos Beltran (knee), Jose Reyes (calf, hamstring) and Carlos Delgado (hip), but Manuel said the team has enough pieces to win without its missing stars.
David Wright agreed.
"I do, and hopefully everybody in here feels the same way. And if they don't, we don't want them here," he said.
Even Santana (9-6) couldn't slow the Mets' spiral after a wacky fourth inning that included an ejection and an easy fly ball that dropped in center field for a double. The ace left-hander also walked two, including Burns on four pitches, and made a wild error.
With a runner on and one out, Corey Hart hit a deep fly but Martinez slipped on the grass and then carved up a divot during his slip while the ball landed untouched about two feet away, giving Hart a double.
Santana then walked J.J. Hardy on four pitches to load the bases, and pitching coach Dan Warthen was ejected by plate umpire Jim Wolf for arguing after a mound visit.
Braun, who drove in Milwaukee's first run with a single in the third, lined an 0-2 pitch over left fielder Gary Sheffield's head, and the relay throw from shortstop Alex Cora bounced away from catcher Omir Santos before he could tag Hardy.
Santana was backing up the play and tried to get Braun, who had rounded third, but Santana's throw went well over the head of Wright, allowing Braun to score easily to make it 5-2.
"When you face a great pitcher like that you need a break or two, and their guy falling down, all those things obviously came back to haunt them," said Braun, who is 7 for 13 against Santana. "Johan's not going to make too many mistakes and he's not going to give up too many runs."
Santana, loser of three of his last four starts, fell to the ground, staring off in disbelief. Martinez, a prized prospect, declined to talk afterward.
"I threw some good pitches and didn't get the calls, and that changed the whole ballgame," Santana said.
In the seventh, Santana gave up Fielder's 20th home run, a long shot to the back of the second deck in right field, before exiting. He allowed nine hits, four walks and five earned runs.
"The things we talked about were all positive things, trying to get back on track and play better baseball," Santana said.
But the runs he gave up were plenty for Burns (1-1), who went 6 2/3 innings to get his first win in place of injured starter Dave Bush (triceps).
"As soon as I got in [to the clubhouse] it felt like about 100 beers on my head," Burns said. "It was the greatest beer bath I've ever had."
Burns' only costly mistake came when Wright hit a two-run homer to give the Mets an early lead. Martinez added his first career homer with two outs in the ninth off reliever Todd Coffey.
"That's a big win. That's something to be proud of," catcher Jason Kendall said of Burns' effort. "That's a pretty good first win over one of the best pitchers to ever play the game."
The Mets went 7-19 in September 2003. ... It was Wright's first homer since June 9.