Absent a year ago and considered a bit of an afterthought until a couple of weeks ago, the Red Sox-Yankees rivalry is back in the September spotlight.

Of course, it never really left its perpetual place on center stage, but the storied rivalry certainly reared its head Thursday night in a big way. With postseason hopes hanging in the air at Yankee Stadium for the opener of a four-game set, the drama unfolded just like old times.

In a tug-of-war played over four-plus hours, the two teams exchanged comebacks in a game the Red Sox took 9-8 in 10 innings, pushing the Red Sox a little closer to an American League East title with the Yankees' most realistic hopes for October remaining a Wild Card berth.

That was just one place the Pulse of the Postseason kept beating toward October on an abbreviated but action-packed Thursday, as races continued to juggle positions in the first week of the final month of the regular season.

That it was all-time saves leader Mariano Rivera giving up the tying run made it an even more remarkable return to the September spotlight for Red Sox-Yankees.

"You don't see that happen too often," said Red Sox slugger David Ortiz, "but it happens. It's part of the game. Playing the game, facing one of the greatest, it seems like you don't have too many chances, but the game isn't over till there's a result, so keep on playing."

By the end of the night, the Red Sox would have their largest division lead since Sept. 2, 2007, while the Yankees stayed in a thick Wild Card race despite their loss.

The way the day began in Kansas City should have been an indication that comebacks and extra innings would be themes for the day. The Royals scored six unanswered runs to erase a big Seattle lead and had the finale of their series against the Mariners seemingly secure heading into the ninth inning. But Raul Ibanez hit a game-tying homer for the Mariners -- and the marathon was on.

Finally, in the 13th inning, just after blasting a long foul, Mike Moustakas delivered the walk-off homer for the Royals for a huge 7-6 win with the AL Central-leading Tigers about come into town.

In the evening games, the National League Wild Card leaders met one more time for the regular season, with the Reds claiming three out of four at home with a 6-2 victory over the Cardinals. That means just 1 1/2 games separate St. Louis in the top Wild Card spot and Cincinnati in the second spot -- a healthy seven games ahead of the Nationals and D-backs.

Meanwhile, the AL Wild Card race became just a little tighter with the Orioles -- 3-1 winners over the White Sox behind three homers, including No. 30 for Adam Jones -- and Royals both winning, and the two leaders losing.

On the West Coast, it was the A's hosting the Astros, with Oakland sharing the AL West and the Wild Card leads with the Rangers, and the Astros owning the fifth and final spot in its first year in the division. But Houston, which took two of three last time into town, took the opener of the four-game set in Oakland, 3-2, dropping the A's a half-game behind Texas in the AL West.

Soon after, the Rays hoped for a sweep but found themselves on the wrong end of a 6-2 decision at Angel Stadium, and the No. 2 Wild Card spot got a little more precarious.

It's turning into baseball's tightest race, and the AL Wild Card will have plenty of opportunity to juggle positions this weekend as the Pulse of the Postseason continues.

Friday's key games to watch (all times ET)

Braves (Minor, 13-5) at Phillies (Lee, 11-6), 7:05 p.m. Preview >
The National League's most dominant team gets back to work, having won eight of its last 10.

Red Sox (Doubront, 10-6) at Yankees (Pettitte, 10-9), 7:05 p.m. Preview >
After a wild opener, the simple fact is the Yankees can't let another one slip away against the hot Sox.

White Sox (Danks, 4-11) at Orioles (Feldman, 11-10), 7:05 p.m. Preview >
The O's would like to take advantage of the matchup after going through five contenders in a row.

Mets (Wheeler, 7-3) at Indians (Kazmir, 7-7), 7:05 p.m. Preview >
Consider this series one of the first that will raise some curiosity with a contender playing in an Interleague matchup.

Dodgers (Capuano, 4-7) at Reds (Leake, 11-6), 7:10 p.m. Preview >
The Dodgers skip Hyun-Jin Ryu for this start and Yasiel Puig's knee is a question mark. The Reds don't figure to mind if the rookies take a little time to recharge.

Nationals (Haren, 8-12) at Marlins (Fernandez, 10-6), 7:10 p.m. Preview >
At seven games behind the Reds in the Wild Card race, the Nationals are up against the wall to reclaim the magic.

Tigers (Sanchez, 12-7) at Royals (Shields, 10-8), 8:10 p.m. Preview >
If ever the Royals wanted a chance to show they're serious about making this year special, a home series against the big, bad Tigers certainly qualifies.

Pirates (Burnett, 7-9) at Cardinals (Kelly, 7-3), 8:15 p.m. Preview >
Home at last, the Cardinals need to catch a new wave of momentum in this wild NL Central race.

Astros (Keuchel, 5-8) at Athletics (Griffin, 12-9), 10:05 p.m. Preview >
The A's won the first 10 meetings between these new AL West foes, but the Astros have won four of the last six.

Rangers (Garza, 9-3) at Angels (Wilson, 14-6), 10:05 p.m. Preview >
The Rangers head into the series as the AL West leaders, and the Angels have been playing well of late.

Rays (Cobb, 8-3) at Mariners (Iwakuma, 12-6), 10:10 p.m. Preview >
The Rays have lost six of their last eight and need to find some traction on this West Coast swing.

D-backs (Corbin, 13-5) at Giants (Petit, 2-0), 10:15 p.m. Preview >
Another win Thursday keeps the D-backs alive, but those NL Central teams are proving hard to catch in the Wild Card race.

If the postseason started today ...

AMERICAN LEAGUE
Wild Card: Rays at A's
Division Series: Wild Card at Red Sox | Rangers at Tigers

NATIONAL LEAGUE
Wild Card: Reds at Cardinals
Division Series: Wild Card at Braves | Pirates at Dodgers

Postseason 101

Magic numbers
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.

Tiebreaker scenarios
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 begins: Oct. 3
AL Division Series begins: Oct. 4
NL Championship Series begins: Oct. 11
AL Championship Series begins: Oct. 12
World Series begins: Oct. 23