ATLANTA -- Call it a battle of the bullpens, or call it an arm barn burner. Whatever the phrase, relievers will loom large over the middle games of the World Series like the gray skies forecast for Truist Park this weekend.

This is the stretch that puts relief staffs to the test. For the second time in as many weeks, the Astros and Braves have to prepare for three games in as many nights. Unlike in the League Championship Series, they’ll also have to battle the rotation attrition that has left Game 4 as a potential bullpen game on both sides.

Add in the threat of inclement weather that could throw a delay into Game 3 on Friday night, plus the lack of a designated hitter in an NL park -- possibly the final times in which Major League hurlers hit -- and the next few games could test both relief corps even more than a typical postseason stretch.

Both teams reached this point by pulling out big games in which their relievers carried the workload. Charlie Morton recorded just seven outs in Atlanta’s Game 1 victory before leaving with what turned out to be a fractured fibula. Houston earned a critical win in Boston in Game 4 of the ALCS with just four outs from starter Zack Greinke, taking a low-scoring duel into the ninth inning before breaking it open.

Which team handles the physical and mental pressure better should have an edge on grabbing a title -- if not this weekend, then in Houston next week. And who has it depends on which aspects matter most:

The bulk factor
Neither team has announced a starter for Game 4, but neither has an ideal scenario. Greinke is the likely candidate for Houston, but he hasn’t thrown three innings in a game since Sept. 19. Atlanta already was looking at a potential bullpen game for Game 4, but now could do the same for Game 5 with Morton out.

“We're going to have probably two games in a row that we're going to have to -- we're going to pitch 18 innings out of that bullpen,” Braves manager Brian Snitker said after Game 2.

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When the Braves last faced such a scenario, Drew Smyly covered 3 1/3 innings and earned the win in Game 4 of the NLCS at Dodger Stadium following Jesse Chavez’s opening inning. Smyly wasn’t as effective in shorter work in Game 2 of the World Series on Wednesday, allowing a Jose Altuve solo homer, walking a batter, hitting another and throwing a wild pitch.

Even before Morton’s injury, the Braves had added length to their bullpen by putting Kyle Wright on the World Series roster. He made two spot starts for Atlanta this year but was a traditional starter at Triple-A Gwinnett. After Morton was injured, the Braves brought up another potential bulk option with lefty Tucker Davidson, who made four starts for Atlanta earlier this season. He made just four appearances for Triple-A Gwinnett due to left forearm inflammation, but he could give the Braves a different look.

The Astros’ long relief strength is more identifiable. Cristian Javier has nine scoreless innings over four appearances this postseason, including three in relief of Greinke in the ALCS.

The workhorse factor
With three consecutive games, somebody will likely need to pitch at least twice -- and probably on consecutive nights. Enter Tyler Matzek, who pitched four times in a five-day span for Atlanta in the NLCS.

Matzek has pitched in 10 of the Braves’ 12 games this postseason, striking out 19 batters over 11 2/3 innings with two wins and four holds. His two perfect innings and four strikeouts against the Dodgers in their NLCS clincher were legendary. He gave up three hits and one run in Game 1 in Houston, but he covered four outs with a four-run lead.

The Astros’ answer is Ryne Stanek, who pitched in Games 2-4 of their Division Series victory over the White Sox and five of six ALCS games against Boston. His work hasn’t been quite as dominant -- and has not included multiple innings -- but he has managed seven scoreless appearances, with single runs allowed in the other two. He has two wins and one hold.

The closer factor
The Braves have not won a game this postseason that Will Smith didn’t throw their final pitch, regardless of margin. The lefty has four saves and earned two walk-off wins while tossing eight scoreless innings on three hits with seven strikeouts. He pitched three consecutive days twice this year, both early in the regular season. By contrast, he hasn’t pitched with Atlanta trailing.

Like Smith, Astros closer Ryan Pressly has only pitched in wins. Unlike Smith, Pressly hasn’t pitched in every win, and he hasn’t always pitched the ninth. Twice this postseason, including Game 2 in Houston, Astros manager Dusty Baker has used Pressly in the eighth inning. When Baker did it in Game 2 of their ALDS win, he cited Kendall Graveman’s versatility. On Wednesday, Pressly pitched the eighth and retired the middle of the Braves' order.

The edge
Both bullpens mix and match well, but the difference might come down to their tasks. While the Astros' bullpen will probably have to cover innings in Game 4, the Braves' relief corps could have to do it in Game 5, too, unless Max Fried starts on short rest. That’s asking a lot. That, plus the Astros’ versatility at the back end, could make the difference in a three-day stretch.