In October, only the best are still playing. Every playoff game is a matchup against a strong opponent. But there are plenty of such tests throughout the year, too. Can we look to those contests for clues to how the postseason will unfold?
In other words: Does a team's performance against other winning teams during the regular season predict postseason success? Do the teams with the best track record against strong opponents win the World Series? Let's take a look.
(For our purposes, "winning teams" means teams with records of .500 or better, and "losing teams" means teams under .500. The winning/losing designation is based on a team's current record, not its record when a specific game or series was played.)
First, here's how the 2019 playoff contenders have performed against winning teams. Records and stats are entering play Wednesday.
1) Dodgers: 45-32 (.584) MLB rank: 1
Won season series against: Braves, Brewers, Nationals, Cubs, Mets
Cody Bellinger has an MLB-leading 1.114 OPS and 27 home runs against winning teams. The Dodgers pitching staff also has an MLB-best 3.69 ERA against winning teams, led by Hyun-Jin Ryu's 2.29, while holding those teams to an MLB-low .683 OPS.
2) Yankees: 43-31 (.581) MLB rank: 2
Won season series against: Dodgers, Twins, Rays, Red Sox
The Yankees can outslug you no matter how good you are. Against winning teams, the Bronx Bombers have the best slugging percentage (.474) and are tied for second in OPS (.802).
T-3) Braves: 52-40 (.565) MLB rank: T-3
Won season series against: Indians, Twins, Cardinals, Nationals, Cubs, Mets
Atlanta has crushed an MLB-high 148 home runs against winning opponents, including 27 by Josh Donaldson (tied for fourth-most individually), 21 by Ronald Acuña Jr. and 19 by Freddie Freeman. Mike Soroka has a 2.96 ERA against those opponents.
T-3) A's: 35-27 (.565) MLB rank: T-3
Won season series against: Yankees, Twins, Rays, Indians, Cardinals
The A's pitching staff has a top-five ERA against .500-plus teams. They won their season series against four of the five other teams in the American League playoff mix.
5) Astros: 35-28 (.556) MLB rank: 5
Won season series against: Indians, Yankees, A's, Cardinals, Cubs
The Astros have the best OPS+ against winning teams -- 121, meaning they're 21% better than the league as a whole. Their pitchers have held those teams to a 75 OPS+ with a 3.81 ERA, both second-best of any team, and they're averaging 10 strikeouts per nine innings, the only team in double digits. No surprise: Justin Verlander (2.06) and Gerrit Cole (2.09) have MLB's two best ERAs against .500-plus opponents.
6) Brewers: 48-40 (.545) MLB rank: 6
Won season series against: Nationals, Cubs, Mets
The Brewers are the fifth-best slugging team against .500-plus opponents. A lot of that was due to Christian Yelich, who posted a 1.111 OPS against those teams with an MLB-high 32 homers. Nineteen of Josh Hader's saves have come against winning opponents.
7) Rays: 37-35 (.507) MLB rank: 7
Won season series against: Astros, Indians, Red Sox
The Rays' 4.06 ERA against .500-plus teams is fourth-best in MLB, and their 9.4 K/9 is fifth-best. Charlie Morton has 119 strikeouts in those games.
8) Cardinals: 41-39 (.513) MLB rank: 8
Won season series against: Dodgers, Nationals, Mets
St. Louis pitchers have a 3.94 ERA against winning teams, third-lowest in MLB, including a 2.76 mark by Miles Mikolas. Jack Flaherty has 135 strikeouts against those opponents.
9) Nationals: 43-48 (.473) MLB rank: 10
Won season series against: Twins, Cubs
The Nats dropped season series to the entire National League playoff field. But Howie Kendrick (1.025), Anthony Rendon (1.015) and Juan Soto (.976) rank 3-4-5 in OPS against winning teams, and Stephen Strasburg has more strikeouts than anybody (145).
10) Twins: 32-37 (.464) MLB rank: 11
Won season series against: Astros, Rays
The Bomba Squad has been much better against losing teams than winning teams, with an .886 OPS (and an MLB-high 188 home runs) against sub-.500 opponents, compared to a .761 OPS against teams .500 or better.
11) Indians: 25-36 (.410) MLB rank: 18
Won season series against: Twins, Yankees
Carlos Santana has risen to the occasion, with a .965 OPS and 16 home runs against winning teams.
Past is prologue?
But now the question is, how much will all this matter in October? That's where things get interesting.
Let's look back at the Wild Card era of postseason play, which began in 1995. Here are the top five teams ranked by performance against winning teams in the regular season: the 2001 Mariners, the 2016 Rangers, the 1999 Braves, the 2002 Braves and the 2013 Braves. You might notice something they have in common -- none won the World Series.
In fact, in the Wild Card era, only one of the 10 teams with the best results against winning opponents, and only three of the top 25, have brought home a championship:
• 1995 Braves (.610 winning percentage, tied for ninth-best)
• 2009 Yankees (.598, 16th)
• 1998 Yankees (.594, tied for 20th)
But what about how each World Series champion stacked up to its postseason peers? Does being the best against strong competition in a given year deliver an advantage against your particular playoff field?
As it turns out, only two of the 24 World Series champions in the Wild Card era have had the best record among their own playoff field against winning teams: the 2009 Yankees and 1995 Braves. Expand it to the top two playoff teams against .500-plus competition in a given year, and you add the 2013 Red Sox, 2004 Red Sox and 1998-99 Yankees.
Extend it to the top three, and you add the three latest World Series champs: the 2018 Red Sox, 2017 Astros and 2016 Cubs.
On the other hand, there have been seven Fall Classic winners since 1995 with losing records against winning teams, most recently in 2014: the 2010 Giants (.446 winning percentage), 2006 Cardinals (.447), 2014 Giants (.466), 2002 Angels (.475), 2008 Phillies (.483), 2000 Yankees (.494) and 2001 D-backs (.494).
Meanwhile, eight champions have had a winning percentage of .550 or higher against winning teams, including last year: the 1995 Braves (.610), 1999 Yankees (.600), 2009 Yankees (.598), 1998 Yankees (.594), 2004 Red Sox (.575), 2018 Red Sox (.554), 2016 Cubs (.554) and 2013 Red Sox (.552).
So don't assume the Dodgers or Yankees will roll to a World Series title just because they beat up on the best in the regular season. Curiously, it seems to be more important to beat up on the worst.
Eight World Series winners in the Wild Card era -- one in three -- have had the best record in their playoff field against teams with losing records (compared to two with the best record against winning teams). That includes last year's Fall Classic winner, and three of the last four:
• 2018 Red Sox (.761 winning percentage vs. losing teams)
• 2016 Cubs (.686)
• 2015 Royals (.667)
• 2010 Giants (.670)
• 2007 Red Sox (.667)
• 2005 White Sox (.667)
• 2002 Angels (.744)
• 1998 Yankees (.776)
Three additional World Series champs have been among the top two playoff teams in their year against losing opponents: the 2013 Red Sox, 2009 Yankees and 1995 Braves. Another pair have been in the top three: the 2017 Astros and 2001 D-backs.
That's 13 of the 24 World Series winners since the beginning of Wild Card postseason play -- more than half.
So how does this year's field of contenders rank against weaker opponents?
1) Twins: 65-23 vs. losing teams (.739 winning percentage)
2) Astros: 68-26 (.723)
3) Indians: 68-28 (.708)
4) Yankees: 59-25 (.702)
5) Dodgers: 56-24 (.700)
6) Nationals: 45-21 (.682)
7) Braves: 44-22 (.667)
8) Rays: 57-29 (.663)
9) Cardinals: 49-29 (.628)
10) A's: 59-36 (.621)
11) Brewers: 39-30 (.565)
Those five top teams, all .700-plus, have been dominant against the teams they're supposed to beat -- powerhouses taking care of business. That list includes the Dodgers and Yankees again, who are just good against everyone, plus the Astros, who joined them as a third 100-win juggernaut. But it also includes the Bomba Squad and the Tribe, who haven't been nearly as good against strong competition.
So what now? There's nothing left to do but watch and see for ourselves how all the October matchups play out.
David Adler is a reporter for MLB.com based in New York. Follow him on Twitter at @_dadler.