Rubuta ci gaba ga wannan sakin layi - Clemens ya fito daga ritaya, ya sanya hannu kan yarjejeniyar shekara guda tare da garinsu na Houston Astros a ranar 12 ga Janairu, 2004, tare da aboki na kusa da tsohon abokin wasan Yankees Andy Pettitte. A ranar 5 ga Mayu, 2004, Clemens ya yi rikodin wasan sa na 4,137 a cikin aikinsa don sanya shi na biyu a jerin duk lokacin bayan Nolan Ryan. An kira shi mai farawa ga ƙungiyar National League All-Star amma a ƙarshe shi ne mai jefa kwallo a cikin wannan wasan bayan ya ba da gudummawa shida a kan hits biyar, ciki har da gudu uku zuwa Alfonso Soriano. Clemens ya gama kakar wasa tare da rikodin 18<unk>4, kuma an ba shi lambar yabo ta Cy Young ta bakwai, ya zama ɗan wasa mafi tsufa da ya taɓa cin nasarar Cy Young yana da shekaru 42. Wannan ya sa ya zama daya daga cikin 'yan wasa shida da suka lashe kyautar a wasannin biyu, tare da Gaylord Perry, Pedro Martínez, da Randy Johnson kuma daga baya Roy Halladay da Max Scherzer suka shiga. Clemens shi ne wanda ya yi nasara a wasan Astros a wasan 7 na 2004 NLCS
a kan St. Louis Cardinals, ya ba da izinin gudu 4 a cikin 6 innings na aiki. Ko da yake ya jefa da kyau, ya gaji a karo na shida, ya ba da gudana hudu.