Thomas rejuvenated his career playing with the Athletics, placing fifth in the American League with 39 HRs and eighth with 114 RBI. He also was key to the team's stretch drive to the playoffs: for the week ending September 10, he was the league's player of the week after hitting .462 with five homers and 13 RBI. The 2006 postseason provided Thomas the opportunity to play in his first postseason games since 2000 due to having missed the 2005 playoffs with an injury, when the Athletics clinched the American League West title, defeating the Seattle Mariners 12–3 on September 26. During the A's first playoff game on October 3, Thomas hit two solo home runs, leading the A's to a 3–2 win over the Twins. His performance during the opening playoff game earned Thomas the distinction of being the oldest player to hit multiple home runs in a postseason game. He led the A's to an ALDS victory, going 5 for 10 with 2 home runs.