In Ronald Koeman’s debut as Ajax coach, John O’Brien entered as a second-half substitute during a 4-0 victory over Fortuna Sittard, which sits at the bottom of the Dutch Honor Divsion. O’Brien entered in the 64th minute with his team already leading by two goals. Koeman, the former Dutch national team defender, replaced Co Adriaanse, who was fired last Thursday with the club trailing first-place Feyenoord and having been ousted from the UEFA Cup by F.C. Copenhagen of Denmark. Tuesday’s win puts Ajax back on top of the standings, but only one point ahead of Feyenoord, four points ahead of Heerenveen and NAC Breda.