MILWAUKEE -- New York Mets star Pete Alonso's three-run, ninth-inning blast off Milwaukee Brewers closer Devin Williams on Thursday night ended a slump for the free agent-to-be while helping send his team to the National League Division Series, where they'll meet the Philadelphia Phillies.

With his team down 2-0, Alonso hit a 3-1 changeup out to right, stunning the home crowd at American Family Field as the Mets won a wild first-round series, two games to one over the Brewers.

"I was just looking for something out over the plate," Alonso said after the 4-2 win. "I just really wanted to hit something hard through the big part of the field. I'm really happy that I capitalized, really happy that I capitalized.

"It's a really special moment."

Alonso was 1-for-11 in the series before his big home run, including hitting into a double play after tripping on his bat as he ran toward first base in Game 2. But he shook that all off, choosing to move on to the next play instead of dwelling on his struggles.

A walk by Francisco Lindor followed one out later by a single off the bat of Brandon Nimmo set the stage for Alonso. He didn't miss his pitch.

"Especially in these big games, you've got to move on to the next pitch and make a positive impact, stay within yourself and execute," Alonso said.

Teammate J.D. Martinez added: "Everyone kind of felt he was due. It's a big monkey off his back. To pick us up was huge. ... He did a great job of not doing too much. It was one of those swings, just point A to point B."

The blast came not long after the Brewers scored the first runs of the game in the bottom of the seventh, on home runs from pinch hitter Jake Bauers and right fielder Sal Frelick. They came on back-to-back pitches, sending Brewers fans into a frenzy.

It didn't last long.

The back-and-forth nature of the game mirrored that of the entire series. According to ESPN Research, over the past five postseasons, teams are 39-2 when leading entering the eighth inning with a chance to clinch a playoff series. The two losses came Wednesday (the Mets) and Thursday (the Brewers) as each team blew leads.

"It was such a great series," Mets manager Carlos Mendoza said. "I'm so proud of this team."

Alonso's heroics came after a masterful performance from Mets starter Jose Quintana, who pitched six shutout innings. He and Brewers rookie Tobias Myers matched each other pitch-for-pitch, neither giving up runs while in the game.

"Tobias was putting up zeros so I knew I needed to," Quintana said while drenched in champagne from the Mets' celebration. "Then Pete did his thing at the right time. I'm so proud of him."

Alonso will be a free agent after the season, which was extended at least three more games. He has played in all 165 that the Mets have competed in this year, hitting 34 home runs during the regular season and now one big one in the postseason.

Despite the daily availability, Alonso didn't have his best year at the plate, as his OPS dropped to a career-low .788. He'll still be sought after come November.

Meanwhile, Mets owner Steve Cohen watched anxiously on a television in the clubhouse in the ninth inning as his first baseman took Williams deep, hearing the crowd before seeing the home run.

"It was on delay," Cohen said with a laugh. "But man he came through. So proud of him."

Cohen said similar about his team, which played a regular-season doubleheader Monday just to get into the postseason, then won Game 1 in Milwaukee on Tuesday before losing Wednesday and then finally winning the series Thursday.

"It feels like we've been on the road for a month," Martinez joked.

The Mets will continue that journey, playing Games 1 and 2 of the best-of-five division series in Philadelphia on Saturday and Sunday.

New York went 6-7 against the Phillies during the regular season and finished six games behind them in the division standings. According to ESPN Research, the 1,081 all-time meetings between the teams are the most between any two franchises without a playoff matchup since 1962.

The matchup never materializes without Alonso's home run.

"We have each other's backs in here," he said. "Tonight was my turn. Tomorrow will be someone else's."