HOUSTON -- The defending American League champions will open the regular season with a stacked lineup, a pair of possible Hall of Famers at the top of the rotation and a bullpen filled with question marks.

The Astros will carry 15 position players and 15 pitchers when they start the regular season Friday against the Mariners with rosters being expanded to 30 at the start of this season. They’ll carry 30 players on their active roster until Aug. 6, at which point they will have to trim their roster to 28. They will carry 28 players until Aug. 20, before going down to 26 for the remainder of the season.

• Astros' 2020 regular-season schedule

With veteran Joe Smith on the restricted list and Brad Peacock and Austin Pruitt on the injured list, the Astros filled out the final spots of their bullpen with inexperienced arms. Enoli Paredes and Brandon Bailey have never pitched above Double-A, and Cristian Javier and Blake Taylor have a combined three games in Triple-A. Taylor is the only left-hander in the 10-man bullpen.

“We do have some guys who are a little short on experience, but they are long on talent,” Astros general manager James Click said. “In addition, given that there aren’t going to be fans in the ballpark for a little while, it may actually be a little easier for these guys to make their Major League debuts or transition to the Major Leagues a little bit better than they can when you’ve got 40-50,000 [people] screaming at you. Ultimately, the decision was based on talent and the guys we thought could help us win.”

Bailey, whom the Astros lost to the Orioles in the Rule 5 Draft only to get back in March, might have been the biggest surprise on the roster. He has struck out 10.4 batters per nine innings with a 3.07 ERA in two seasons in the Houston system. He posted a 3.30 ERA in 22 games (17 starts) last year at Double-A Corpus Christi. He was added to Houston's 40-man roster.

“Just the ability to throw strikes,” Click said. “The command was very impressive. The heart. We’re going to need him to soak up some innings for us from time to time, but it’s also an opportunity for him to show what he can do and earn his way into a bigger role.”

The players that did not make the Astros’ 30-man roster, and all players on the IL, will report to Corpus Christi this week, where they will continue to train as part of the Astros’ player pool. Houston will have to identify a three-man traveling taxi squad before its first road game July 31.

Here’s a position-by-position breakdown of the roster:

Catchers (3)
Martín Maldonado, Dustin Garneau, Garrett Stubbs

The Astros re-signed Maldonado to a two-year contract after acquiring him at the Trade Deadline each of the previous two seasons. Houston signed Garneau in November, meaning Maldonado and Garneau will handle most of the catching duties. Stubbs can play some outfield and maybe some infield, too, and his flexibility and speed got him on the roster.

First base (1)
Yuli Gurriel

Gurriel is back after having the best season of his career, during which he hit .298 with 31 homers and 104 RBIs and was an AL Gold Glove Award finalist. In November, Gurriel agreed to a contract for 2020 worth $8.3 million, up from the original $8 million, with an opportunity to earn $250,000 more in bonuses. As was determined when he signed his original five-year, $47.5 million deal in 2016, he will become a free agent after the '20 season.

Second base (1)
Jose Altuve

Altuve rebounded from a right knee injury and had a strong 2019 season, hitting .298 with 31 homers and 74 RBIs. He led the AL in hits and total bases after the All-Star break. Altuve signed a long-term contract extension prior to the '18 season.

Shortstop (1)
Carlos Correa

Correa played only 75 games in 2019, after two stints on the injured list with a fractured rib (May 29-July 26) and back discomfort (Aug. 21-Sept. 17), but he produced when he was healthy, hitting .279 with 21 homers and 59 RBIs.

Third base (2)
Alex Bregman, Abraham Toro

Bregman had a strong 2019 season, hitting .296 with 41 homers, 112 RBIs, 119 walks and only 83 strikeouts. He led the AL in walks and was second in on-base percentage (.423). Toro started 20 games last August and September at third base in his first big league action.

Utility (2)
Aledmys Díaz, Jack Mayfield

Díaz played in only 69 games last season, but he started 18 games at first, 16 at second, 15 at third, three in left and two at shortstop. The undrafted Mayfield appeared in 26 games in his Major League debut last year and can play shortstop and second base. 

Outfield (5)
Michael Brantley, George Springer, Josh Reddick, Kyle Tucker, Myles Straw

The Astros traded Jake Marisnick to create some room in a crowded outfield that now includes Tucker, who figures to assume a starter role next year. With slugger Yordan Alvarez out, most of Tucker’s at-bats could come at designated hitter. Straw brings elite speed and strong defense, as well as the ability to play shortstop. 

Designated hitter (0)

Alvarez, the 2019 AL Rookie of the Year Award winner, was placed on the injured list July 12 for undisclosed reasons and won't be ready to start the season. The DH duties will be spread around to begin the year, with Tucker likely facing right-handers quite a bit and Díaz as a main option against lefties.

Starting pitchers (5)
Justin Verlander, Zack Greinke, Lance McCullers Jr., Josh James, Framber Valdez

McCullers is back after missing the entire 2019 season following Tommy John surgery, joining Verlander and Greinke in an elite top of the rotation. José Urquidy was a given to be in the rotation in spring, but he is now on the injured list for undisclosed reasons. James carried a strong spring through Summer Camp to win the fourth spot, and Valdez will be the only lefty in the rotation.

Relievers (10)
Roberto Osuna, Ryan Pressly, Joe Biagini, Chris Devenski, Bryan Abreu, Cy Sneed, Blake Taylor, Cristian Javier, Enoli Paredes, Brandon Bailey

Opportunities abound for youngsters like Abreu, Taylor, Javier, Paredes and Bailey, a group that has a combined seven games in the big leagues (all by Abreu last year). Osuna and Pressly are elite back-end relievers when healthy, and there’s some uncertainty about Osuna’s readiness for Opening Day. Devenski and Biagini will have to take a step forward this year. Sneed will be a primary long-relief option.