Mookie Betts got the right hit at the right time -- for him and the Red Sox

Red Sox come from behind to walk off (1:08)

Boston scores three runs in the ninth, which includes Mookie Betts' walk-off two-run double to propel the Red Sox 5-4 over the Cardinals. (1:08)

BOSTON -- Down to his very last strike, with the Boston Red Sox down to their final out in the bottom of the ninth inning on Wednesday night, Mookie Betts laid off back-to-back sliders that narrowly missed clipping the outside corner of the plate.

Talk about a couple of hot takes.

A month ago -- even as recently as two nights ago -- Betts probably would have swung at either pitch. And in all likelihood, he would have missed them. Or maybe he would have lunged far enough over the plate to pop them up. It has been that kind of month for Betts, who was last season's American League MVP runner-up but has been a .262 hitter with seven extra-base hits since the All-Star break.

But when St. Louis Cardinals reliever John Brebbia, a rookie who grew up a half-hour south of Fenway Park in Sharon, Massachusetts, tried to get Betts to go fishing for a slider, the Red Sox star didn't bite.

"It was huge," Betts said. "It changed the whole at-bat. I was able to force him to throw a strike, and any time I can get a strike, I have a better chance of getting good wood on it. Being able to lay off those definitely gave me a better opportunity."

With Betts having worked the count full, Brebbia threw another slider. This one, though, was over the plate, and Betts drove it off the top of the AL East standings that are posted on Fenway Park's fabled Green Monster. Chris Young scored easily from second base, and Jackie Bradley Jr. motored home all the way from first, diving back to touch home plate after Cardinals catcher Yadier Molina couldn't handle the relay throw.

The Red Sox came all the way back, too. Trailing by two runs entering the ninth inning, they rallied for a 5-4 win -- their ninth walk-off victory of the season and eighth since June 12. With a day off Thursday, Boston is assured of opening a three-game series against the second-place New York Yankees with no less than a four-game lead in the division.

"It's coming down to the final months. We have to play good as a team," said shortstop Xander Bogaerts, who started the comeback with his first homer since July 5, a leadoff shot in the ninth against Cardinals closer Trevor Rosenthal. "That was a great win to go into the off day. That changes a lot of things as opposed to if we had lost today."

Betts could be a game-changer, too. It's not that he has had a bad season. Most players would happily swap their numbers for his: .269 average, 34 doubles, 18 homers, 75 RBIs, 17 stolen bases, .796 OPS. Based on wins above replacement as calculated by FanGraphs, he has been the league's fourth-best position player.

Some of that is due to Betts' success with runners in scoring position. He has been one of the Red Sox's best clutch hitters, batting .390 (39-for-100) with 55 RBIs with men on second or third base -- a success rate that manager John Farrell attributes to heightened focus.

"I can't even explain what's going through my head when I step in the box," Betts said. "Right now, I could tell you something, but when I'm in the box, it's probably something different. I'm not exactly sure if it's extra focus or anything. I'm trying to do good all the time, but if that's the side I'm going to err on, I'll be happy with that."

Betts hasn't been happy with his season, though, especially when he compares it to last year. He says he has been too inconsistent, with not enough hot streaks, and cold spells that have lasted too long. And rather than repeating his MVP credentials from last season, he has been surpassed as a front-runner for the award by Houston Astros second baseman Jose Altuve and others.

The biggest problem? As Farrell sees it, Betts has chased pitches -- sliders, in particular -- off the plate that he was taking last year. He still has nearly as many walks (54) as strikeouts (56), a sign that he's being selective enough. But he hasn't hit the ball as hard as he normally does.

"There's been times where it looks like he gets a little pull-happy and there's some balls in the air," Farrell said. "I can't say that he's expanding the strike zone wholesale. That's not the case. He and a couple other guys, we're still trying to have them hit stride, which they haven't yet for a lengthy period of time."

Put Bogaerts in that category since he bruised his right hand July 6 at Tampa Bay. But Bogaerts notched three hits Tuesday night before taking Rosenthal deep.

Perhaps Betts' three-hit game Wednesday night, capped by his best at-bat in weeks, will get him going, too.