At the 2008 Summer Olympics in Beijing, Lezak was the oldest male on the U.S. swim team. He anchored the U.S. 4×100-meter freestyle relay team that won the gold medal and set a new world record. At the start of the leg, Lezak trailed French anchor Alain Bernard by nearly a full body length. In the final 25 meters, with Bernard still leading by half a body length, Lezak overtook Bernard. At the time, Lezak's split of 46.06 was the fastest 100-meter freestyle split ever by nearly 0.6 seconds (at the 2019 World Championships Duncan Scott swam a 46.14 in the 4×100-meter freestyle relay to reduce that margin to 0.08 seconds). The American team's final time of 3:08:24 was just 0.08 seconds ahead of the French team's 3:08.32, making it the closest finish in the event's history. Both teams finished nearly four seconds ahead of the previous world record.