HOUSTON -- Two of the most memorable debut seasons in Astros history came from hotshot sluggers who went on to win Rookie of the Year -- Jeff Bagwell in the National League in 1991 and Yordan Alvarez in the American League in 2019. But it would be hard to top the impact three legendary pitchers had in their Houston debuts.

After coming out of retirement in 2004, Roger Clemens helped launch Space City into the baseball stratosphere. And there were the blockbuster trades to acquire former Cy Young winners Randy Johnson (1998) and Justin Verlander (2017), where both aces worked their magic for the Astros down the stretch and into the playoffs.

So, here are the top five individual debut seasons in Astros history:

1. Roger Clemens, 2004
On the heels of Andy Pettitte signing with his hometown Astros prior to the ‘04 season, Clemens followed him from the Bronx to his home city of Houston, taking baseball excitement to a fever pitch at Minute Maid Park. The 41-year-old Clemens continued to defy Father Time, winning his record seventh Cy Young Award in his 21st season in the big leagues. Clemens went 18-4 with a 2.98 ERA in 33 starts with the Astros and became the fourth pitcher to win the Cy Young Award in each league.

Clemens became the oldest pitcher (42) to win a postseason game with a victory in Game 1 of the NL Division Series against the Braves while helping the Astros win their first playoff series in history. He was 9-0 with a 2.08 ERA in his first 12 starts with the Astros and moved into second place on the all-time strikeout list on May 5 when he fanned Raul Mondesi for career strikeout No. 4,137. He also finished the season tied for 10th on the all-time wins list with 328.

Clemens had announced his retirement following the 2003 season with the Yankees, but the talk in Houston was about a comeback. Two days before Christmas, Astros owner Drayton McLane and his wife paid a visit to the Clemens home in the Memorial area of Houston and gave them a small glass baseball glove ornament as a gift. They started talking.

“It was complicated because he had fully retired, and we persuaded him to come back,” McLane said.

2. Justin Verlander, 2017
Former Astros general manager Jeff Luhnow pulled off a stunning trade in the minutes before the Aug. 31 Deadline, acquiring Verlander from the Tigers in exchange for prospects. Verlander, of course, had to approve the trade and wasn’t sure he wanted to leave Detroit after a decade-plus of building a resume as a Tigers legend.

What’s more, Houston had just been devasted by Hurricane Harvey, which further complicated matters. Astros pitcher Dallas Keuchel made a recruiting call to Verlander and he soon agreed to waive his no-trade clause -- a move which changed the course of baseball history in Houston. Verlander went 5-0 with a 1.06 ERA in five regular-season starts for the Astros and carried his hot hand in the postseason.

He made his first career relief appearance by throwing 2 2/3 innings in Game 4 of the ALDS clincher against the Red Sox and won both of his starts in the ALCS against the Yankees. He was named the Most Valuable Player of the ALCS. The Astros won the 2017 World Series, beating the Dodgers in seven games, with Verlander starting two of those.

“The opportunity to come play for a championship-caliber team -- for not only this year but for the remainder of my contract -- is ultimately what it really came down to,” he said.

3. Randy Johnson, 1998
With the 1998 Astros chugging towards a then club-record 102 wins, former general manager Gerry Hunsicker knew he needed to go for it. Hunsicker landed the Big Unit from the Mariners just before the July 31 non-waiver Trade Deadline in a move that stunned baseball fans in Houston.

“When you have a good team,” Hunsicker said, “pile on to give yourself as much reinforcement as you can to get through the playoffs, and, of course, that year the Yankees were arguably the best team in the American League and they had a lot of talented left-handed hitters, and adding a dominant left-handed starter like Randy Johnson really would give us a great chance against them if we got to that point.”

Johnson, acquired for two top prospects (Freddy Garcia and Carlos Guillen, as well as John Halama), was nothing short of magnificent for the Astros. He made 11 starts and went 10–1 with a 1.28 ERA. The Astrodome was filled to capacity every time he started. He was a rock star with a mullet.

“I was going from the Kingdome, which was a band box, and now I was pitching in the Houston Astrodome,” Johnson said. “I was also going and playing for a first-place team. Billy Wagner was my closer. So everything just kind of fell into place, and it was my best two months of my career.”

Alas, the Astros never got a chance to face the Yankees despite two great starts from Johnson in an NLDS loss to San Diego. He signed a four-year, $52.4-million deal with the D-backs in the offseason and wound up winning four Cy Young Awards. But the two-month stretch in Houston remains legendary.

4. Yordan Alvarez, 2019
The Cuban slugger, acquired in 2016 from the Dodgers in exchange for relief pitcher Josh Fields, began 2019 by hitting 23 homers in 56 games at Triple-A Round Rock before the Astros called him up June 9. He quickly became one the most dangerous bats in the middle of perhaps the best lineup in baseball.

With great plate discipline and prodigious power, Alvarez hit .313 with 27 homers, 78 RBIs and set a Major League rookie record with a 1.067 OPS in 87 games, winning the AL Rookie of the Month in each of his first three months in the big leagues. Not surprisingly, he was a unanimous pick for AL Rookie of the Year.

Alvarez, 22, homered in his second Major League at-bat and didn’t slow down for months. He hit seven homers in his first 12 games, which is a club record, and set a Major League record by posting 51 RBIs in his first 45 games. He led all MLB rookies in extra-base hits (53), on-base percentage (.412) and slugging percentage (.655). Alvarez’s 178 WRC+ tied for second among rookies in the live-ball era (since 1920), trailing Willie McCovey’s 185 in 1959.

5. Jeff Bagwell, 1991
Acquired by the Astros from the Red Sox at the Trade Deadline in 1990 for veteran relief pitcher Larry Andersen -- one of the most lopsided deals in MLB history -- Bagwell began a 15-year Hall of Fame career by winning the NL Rookie of the Year in 1991.

A skinny third baseman who was blocked in Boston’s system, and with Ken Caminiti established at third base in Houston, the Astros shifted Bagwell across the diamond to first base. He was in the Opening Day lineup in 1991 and would be for 15 consecutive seasons. He hit .294 with 15 homers and 82 RBIs in 156 games in his rookie season.

“The fact he was Rookie of the Year for me, that was a pretty good sign of things to come,” said Art Howe, who managed the Astros from 1989 to 1993. “I think it was his first game in the big leagues against the Cincinnati Reds, and the ‘Nasty Boys’ were pitching against us and I think they had the lead and he’s leading off the top of the ninth. [Rob] Dibble’s on the mound and he’s blowing them away and he knocks Bagwell down. I don’t know how he got out of the way of it. The next pitch, [Bagwell] hit a rocket up the middle. That told me we had our hands on a great player.”