Zaun hit a game-ending grand slam in the 13th inning and Toronto beat the Rays 7-4 on Saturday to extend their season-high winning streak to seven.
The Rays are 1-4 this month, allowing Boston to cut into their AL East lead, but manager Joe Maddon isn't worried about his young team.
"You're going to lose games like this," Maddon said. "When you get into the playoffs, you're going to lose some tough games and you've got to come back tomorrow. That's why it's 162, that's why they call it a grind. Sometimes you get your heart broken for about 30 minutes but you've got to put it back together, come back tomorrow and play another game and that's what we'll do."
The Rays won a franchise-record 21 games in August, but have stumbled since, dropping back-to-back series for the first time since a seven-game losing streak immediately before the All-Star break. Until they lost two of three to New York Yankees earlier this week, Tampa Bay hadn't lost a series in the second half.
Despite the loss, Maddon's optimism was echoed in the clubhouse.
"We were playing very well and we ran into the Yankees and they took two of three from us," outfielder Rocco Baldelli said. "That happens. It's such a small sample size the last four or five games, you can't let five games symbolize the way the season is going. We feel like we're going to come out tomorrow and win."
Closer Troy Percival (2-1) served up Zaun's slam, but said he expects the Rays to bounce back.
"We've been counted out all season, we were supposed to come in last place all season and we've been pretty defiant," Percival said.
The Rays entered with a 2½-game advantage over the Red Sox, who carried a four-game winning streak into their matchup with Texas on Saturday night.
Lyle Overbay added two solo homers for Toronto, which matched its longest winning streak since Sept. 22-29, 2002.
Tampa Bay tied it with three runs in the ninth and Dioner Navarro's RBI single off Brian Tallet (1-1) in the 13th inning gave the Rays a 4-3 lead. But Toronto rallied against Percival in the bottom half.
Vernon Wells and Brad Wilkerson got it started with consecutive one-out singles. Overbay grounded into a fielder's choice and Scott Rolen walked before Zaun went deep for his sixth homer of the season and fourth career slam.
"I was trying to go with a fastball away right there and I pulled it across the plate," Percival said. "Missed location, bad pitch."
Zaun finished 3-for-5, picking up his first hit since July 30. He went 0-for-19 in eight August appearances.
"If I hit it anywhere else it's a game-ending flyball," Zaun said of his shot into the right-field bullpen. "I got it far enough down the line, it got over and they all count. It was a big moment. That was a lot of fun."
Percival and Blue Jays closer B.J. Ryan each picked up their fourth blown save. Baldelli connected for a pinch-hit, two-run homer off Ryan in the ninth and pinch-runner Fernando Perez scored on second baseman Joe Inglett's error to tie it at 3.
Overbay hit a leadoff drive in the second and an opposite-field shot to left in the fourth for his 14th homer, helping Toronto build a 3-0 lead. It was his seventh career multihomer game and second this season.
Shaun Marcum was in line for his ninth win before Tampa Bay's rally. He allowed four singles, walked three and struck out seven in seven innings.
James Shields allowed three runs and six hits in eight innings for the Rays.
- Rays 3B Evan Longoria (fractured wrist) was activated off the 15-day DL before the game. Longoria felt no pain after swinging a bat earlier Saturday and plans to resume batting practice Monday.
- Zaun snapped an 0-for-21 skid with a single in the second.
- Inglett's error was his second in as many games.
- The Blue Jays used nine pitchers, while the Rays used six.
- It was the first time in franchise history the Blue Jays hit a game-ending grand slam in extra innings.