DC SPAN! @thisisdspan shoots one through Simmons' legs, both runs score. #Nats walk-off, 6-5!
- Washington Nationals (@Nationals) September 17, 2013
Meanwhile, at PNC Park, the Pirates took a 5-2 loss to the Padres, falling out of a tie for the NL Central's top spot. The Cardinals, in first place alone with Pittsburgh's loss, erupted for six third-inning runs en route to an 11-4 win over the Rockies that extended their Central lead to a game.
In the American League, the Rangers snapped a seven-game losing streak with a 7-1 win over the Rays, with whom they're once again locked in a flat-footed AL Wild Card tie.
The AL East-leading Red Sox entered Tuesday with a chance to clinch a postseason berth -- with a victory and a Royals win over Cleveland -- but Boston dropped its series opener with the Orioles, who remained in the thick of the AL Wild Card race with their 3-2 win.
The Indians sit a half-game behind the second AL Wild Card berth thanks to a come-from-behind, 5-3 win over the Royals, who fell to 3 1/2 games back with the loss.
The Wild Card-hopeful Yankees were looking forward to facing the struggling Blue Jays, but they were silenced at Rogers Centre by knuckleballer R.A. Dickey, who earned his 13th win of the year. New York is even with Kansas City, 3 1/2 games out.
The Tigers got closer to AL Central pay dirt by topping the Mariners, 6-2, and the Dodgers are in solid clinching range by beating the D-backs, 9-3, in a game that saw Los Angeles jump out with four first-inning runs against Patrick Corbin.
The A's bounced back against the Angels with a walk-off, 2-1 win and are closing in on their second straight AL West title.
If the postseason started today ...
Wild Card: Rays at Rangers
Division Series: Wild Card at Red Sox | Tigers at A's
Wild Card: Reds at Pirates
Division Series: Wild Card at Braves | Cardinals at Dodgers
To calculate a team's magic number, take the number of games it has remaining and add one. Then subtract the difference in the number of losses between that team and its closest pursuer.
A tiebreaker game will be played to determine a division winner, even if the tied clubs are assured of participating in the postseason. If a division championship tiebreaker is necessary, the head-to-head record between the clubs will determine home-field advantage. If the head-to-head record is tied, then division record will be the next tiebreaker.
If two clubs are tied for the two Wild Card berths, home-field advantage will be determined by the head-to-head record between the clubs. If the head-to-head record is tied, then division record will be the next tiebreaker.
• Tiebreaker rules »
2013 postseason schedule
NL Wild Card Game: Oct. 1
AL Wild Card Game: Oct. 2
NL Division Series begin: Oct. 3
AL Division Series begin: Oct. 4
NL Championship Series begins: Oct. 11
AL Championship Series begins: Oct. 12
World Series begins: Oct. 23