Every game has a turning point, where one team takes a big leap toward victory, whether it's a towering home run, a squeeze bunt, a bases-loaded strikeout or a run-saving catch.
Thanks to a metric called win expectancy, we can attach numbers to these swings in fortune. Expressed as a percentage, win expectancy shows a team's chances of victory at a particular point in time. This is based on historical data that shows how clubs have fared in different situations, based on factors such as the score, the inning, how many outs there are and which bases are occupied.
Using win expectancy as a guide, here is a look at three plays that served as turning points in Friday's games:
Rivera rips a double to tie things up at Citi Field Game: Marlins at Mets
Situation: With the bases loaded and nobody out in the seventh inning, New York's T.J. Rivera faced veteran sidearmer Brad Ziegler with the Mets trailing, 7-5.
Result: Rivera drilled a first-pitch sinker from Ziegler down the left-field line for a two-run double, tying the score at 7. The Mets went on to win, 8-7.
Win expectancy for Mets: +29.6 percentage points (51.4% to 81.0%)
Facts to know:
• Rivera's double had an exit velocity of 105.5 mph according to Statcast™, his hardest-hit ball this season. It was Rivera's second hardest-hit ball in the Statcast™ era (since 2015) -- he hit a 105.6-mph single against the Phillies on Sept. 30, 2016.
• When the bottom of the seventh began, the Mets' win expectancy sat at 5.9 percent. But over the span of the next six batters -- each of whom recorded a hit -- that jumped to 81 percent after the Rivera double.
They said it: "That situation, you just try to slow things down," Rivera said. "Everything starts to speed up a little bit. Runners are on base, and you've got to drive them in. I wanted something up ... and it happened on the first pitch. ... It's a great feeling to come through in the situation where your team needed you."
Morales mashes second homer to break tie at Tampa Bay Game: Blue Jays at Rays
Situation: With the score tied at 4 in the top of the eighth, Kendrys Morales -- who had already homered an inning earlier -- came to the plate against Rays right-hander Jumbo Diaz with runners at first and third and two outs.
Result:: Morales smashed a 99-mph fastball on a 2-2 pitch from Diaz deep into the right-field seats for a three-run homer. He drove in five runs in the 8-4 Toronto victory.
Win expectancy for Blue Jays: +42.3 percentage points (50.2% to 92.5%)
Facts to know:
• Entering Friday's contest against the Rays, Morales had just two extra-base hits (a double and a homer) in his previous 13 games, dating back to April 21st. He had a double along with his pair of homers Friday.
• Morales' first home run resulted in another significant jump in win expectancy for Toronto. Just as with his three-run shot in the eighth, Morales followed a Russell Martin walk with a two-run homer to tie it at 3 in the seventh. That increased the Blue Jays' win expectancy by 26.8 percentage points, from 23.2 percent to 50.0 percent.
They said it: "It was a good day for me," Morales said. "I just made good contact and put the barrel on the ball, and it went far."
Down to final strike, Gardner hits go-ahead homer at Wrigley Game: Yankees at Cubs
Situation: With two outs in the top of the ninth, and the Yankees trailing the Cubs, 2-0, Brett Gardner stepped to the plate with runners at first and second. Cubs reliever Hector Rondon, trying to close the game out with Wade Davis having pitched in three straight games, worked a 2-2 count on Gardner.
Result: Rondon threw an 83-mph slider that Gardner lofted into the right-field seats for a three-run homer. Aroldis Chapman closed out the bottom of the ninth for a 3-2 Yankees win.
Win expectancy for Yankees: +73.7 percentage points (7.3% to 81.0%)
Facts to know:
• Prior to Friday's home run at Wrigley, Gardner had never hit a go-ahead homer (not including his two career walk-off homers) later than the seventh inning -- he hit a solo shot in the top of the seventh against Red Sox reliever Matt Albers to break a 1-1 tie at Fenway Park on Aug. 7, 2011.
• Just five of Gardner's 65 career home runs entering this week had come on sliders, but he's hit two in the last four days. Before his dramatic three-run shot on Friday, Gardner hit a solo homer against Blue Jays right-hander Mat Latos at Yankee Stadium last Tuesday. Both pitches were in almost identical locations -- at the knees and on the inner-half of the plate.
They said it: "It was the right pitch, but it wasn't in the right spot," Cubs catcher Willson Contreras said on Gardner's homer. "[Rondon] missed by this little bit, and he paid for it."
Manny Randhawa is a reporter for MLB.com. Follow him on Twitter at @MannyOnMLB. This story was not subject to the approval of Major League Baseball or its clubs.