There are few things better than traditional rivals battling each other for postseason position in late September. So while five of baseball’s six divisions seem essentially wrapped up, and the wild-card field in both leagues is coming down to just a handful of teams, the next 10 days should spark plenty of interest thanks to two rivalries that are nearly as old as baseball.

In the National League West, the San Francisco Giants are trying to hold off the Los Angeles Dodgers for the division title — and the chance to avoid the volatility of a single-elimination wild-card game. In the American League, the Yankees and the Boston Red Sox — who face each other in a three-game series that starts Friday — are fighting for one of the two open wild-card spots, with a very real chance that one of them misses the playoffs.

A look at the open races shows a little room for movement as things wind down, with just enough tension to keep things fun.

American League Wild Card

Both teams have had ups and downs this season, but with nine games left for each, the Red Sox (88-65) lead the Yankees (86-67) by two games for the A.L.’s top wild-card spot. Just a half-game behind the Yankees — so currently not in line for a postseason spot entering Thursday’s game — are the surging Toronto Blue Jays (85-67), a team with a top candidate for the Cy Young Award in Robbie Ray and a run differential (+171) greater than the teams ahead of them combined (+118).

This weekend’s series in Boston could provide some clarity. On Friday, it will be ace vs. ace, as Gerrit Cole of the Yankees faces off against Nathan Eovaldi of the Red Sox. Saturday’s game will see a steep downturn in star power, with Nestor Cortes starting for the Yankees against Nick Pivetta. Sunday night’s game will be somewhere in the middle, with Jordan Montgomery going up against Eduardo Rodriguez.

A sweep by either team would tilt the race significantly, and the Red Sox and Yankees beating each other up could be good news for the Blue Jays, who start a four-game series in Minnesota on Thursday and will host the Yankees in Toronto next week.

Is it fair that one of these teams will be left out of the postseason when all three would be easily leading the N.L. East and be fighting for the division title in the A.L. Central? No. But that’s the reality of the format.

National League West

The Giants (99-53), who had been written off by most pundits ahead of the season, have cruised through the regular season, being the first team to 70, 80 and 90 wins. They will be the first to 100 as well, and they’ve done it through a combination of throwback seasons from stalwarts of the team’s glory days and breakout seasons from unheralded acquisitions. They’ve hit so many home runs that Ron Wotus, the team’s third-base coach, may be running out of different ways to high-five people.

That leaves the defending champion Dodgers (97-55) in line for a wild-card spot despite having the second best record in baseball. For an idea of how out of place it is as a wild-card contender, rather than a division leader, Los Angeles has a 14½-game lead over the No. 2 team in the wild-card race (St. Louis) and a 19-game lead over the No. 3 team (Cincinnati).

Thanks to the acquisition of Max Scherzer and the return from injury of Clayton Kershaw, it is easy enough to assume the Dodgers will be a nearly unstoppable force once October rolls around, but that will all hinge on the luck of a single wild-card game unless they are able to overtake San Francisco for the division lead.

Both teams have it relatively easy down the stretch, as they each get a chance to beat up on lowly Arizona and mediocre San Diego. But helping San Francisco considerably is that its third opponent in the next 10 days is the Colorado Rockies (71-80); the Dodgers have to close with three games against a strong Milwaukee team that may be motivated to finish on a high note.

The good news for baseball is that a win in the wild-card round by either the Giants or the Dodgers would set up a thrilling division series between 100-win rivals. The bad news is that no situation exists in which both teams survive beyond that round.

The Rest of the Races

The Chicago White Sox (85-66) wrapped up the A.L. Central in spring training, the Tampa Bay Rays (94-59) should close out the A.L. East soon and the Houston Astros (91-61) have no real challenger in the A.L. West. The Milwaukee Brewers (91-61) built a big enough lead in the N.L. Central that a surge from the St. Louis Cardinals (82-69) should be fruitless.

That leaves the only real hopes for movement, behind the N.L. West and the A.L. wild card, in the N.L. East, where the Philadelphia Phillies (78-74) are trying to challenge the Atlanta Braves (80-70), and the second N.L. wild card, where the Cincinnati Reds (78-74) have fallen a bit too far behind the Cardinals.