Officially, Yordan Alvarez missed the Houston Astros' first 18 games of the season for undisclosed reasons.

However, Alvarez admitted when he rejoined the team Friday that he was sidelined while recovering from the coronavirus.

Alvarez homered Friday in his first at-bat of the season, a three-run shot into the Crawford Boxes in left field, sparking a nine-run first inning as the Astros defeated the visiting Seattle Mariners 11-1.

The reigning American League Rookie of the Year said he kept quiet about having the disease because he didn't want to worry his family in Cuba, though he told his parents.

"This has been a couple of difficult months for me," Alvarez said. "I know the team didn't say anything about it, but I did test positive for coronavirus. I had headaches and stuff like that, but thank God I'm feeling a lot better and I was able to get ramped up and feeling really good to be back with the team."

Alvarez said he tested positive two days before the start of the Astros' summer camp. His wife, Monica, also had the disease and was asymptomatic, but his young daughter, Mia, remained coronavirus-free.

"Yeah, obviously, it's a scary situation for me, especially with my daughter, because I'm in contact with her every day," Alvarez said. "And I'm playing with her all the time, so it's a scary situation knowing that you're that close to your family and to have the virus is obviously scary at the outset."

Alvarez had a chance to do even more damage in the first inning. He later came up with the bases loaded and grounded into a double a ball hit 111.7 mph, the hardest hit of the inning.

Alvarez was hit by a pitch with the bases loaded in the fifth inning, capping the scoring.

"He said he was ready to go," Astros manager Dusty Baker said. "I called him (Thursday night), and he said he had his bags packed and was ready to come back."

Alvarez was a welcome addition to a struggling Houston offense. He hit .313 with 27 homers and 78 RBIs last year in 87 games and was a unanimous selection as the league's top rookie. His 1.067 on-base-plus-slugging percentage set a major league record by a rookie in a single season.

"He walked into the clubhouse and everybody was very happy," Baker said.

Right-hander Cristian Javier (1-1, 4.02 ERA) is scheduled to start Saturday against the Mariners, whom the Astros have defeated in 17 of the past 18 games.

The Mariners plan to send lefty Nick Margevicius (0-0, 3.24 ERA) to the mound.

Both Javier and Margevicius made their only career appearances in this rivalry when they pitched a scoreless inning of relief when the teams played a four-game series at Minute Maid Park to open the pandemic-shortened season last month.

Seattle was scheduled to start Yusei Kikuchi on Friday in the series opener, but he was scratched less than an hour before the game due to neck spasms. Fellow lefty Nestor Cortes lasted just one-third of an inning, allowing eight runs (seven earned).

"It's not a fun situation to be in," Mariners manager Scott Servais said. "It happens throughout the course of the season, you're going to have a game or two like that.

"You lose the starter like that, there are not many teams that are going to be able to rebound and have somebody step in and give you five innings. You are just hoping to take it an inning at a time, and we weren't able to get through that first inning."

--Field Level Media