O'Leary broke numerous appearance records at Arsenal; he was the youngest person to reach the 100- and 200-match milestones, and he made his 400th appearance while still only 26. He passed George Armstrong's all-time record of 621 first-team games in November 1989. By this time, O'Leary was no longer automatic first choice (with the partnership of Tony Adams and Steve Bould at the centre of George Graham's defence), but he still turned in over 20 appearances as Arsenal won the 1988–89 First Division title due to a 2–0 win at Anfield on the final day of the season.