10. Dallas Keuchel – 2015
Keuchel established himself as a major league starter in 2014 and then broke out in 2015 by winning the AL Cy Young award. He went 20-8 with a 2.48 ERA, striking out 216 batters in a league-leading 232 innings. He made his first All-Star team and won his second straight Gold Glove, totaling 6.5 WAR.
9. Gerrit Cole – 2019
You might be surprised to see Cole this low, but 6.6 WAR is an excellent season. There have just been eight better ones. Cole went 20-5 with a league-best 2.50 ERA, setting a franchise record with 326 strikeouts and finishing second in the Cy Young voting.
8. Mike Hampton – 1999
Hampton’s 22 wins still stand as the franchise record in a single season, and he led the league in winning percentage after suffering only four losses. He finished second in the Cy Young voting and won a Silver Slugger, tossing 239 innings of 2.90-ERA ball and hitting .311 at the plate, totaling 6.7 WAR.
7. Joe Niekro – 1982
Niekro had a couple of 20-win seasons with top-four Cy Young finishes with the Astros, but this wasn’t one of them. He did put up a career-best 2.47 ERA, though, to go with a 17-12 record in 270 innings over 35 starts. This performance was worth 6.8 WAR.
6. Andy Pettitte – 2005
Pettitte’s first season in Houston was cut short due to injury, but he rebounded with a 2.39 ERA in 33 starts, putting up a 17-9 record. He finished fifth in the Cy Young voting and helped the Astros reach their first World Series, compiling 6.8 WAR along the way.