Former champion Rory McIlroy exploited ideal conditions to climb the leaderboard on day three of the 149th Open at Royal St George's.
That meant an early tee time on Saturday morning, but there were still thousands of spectators on the course as McIlroy holed from 12 feet for birdie on the first and twice the distance on the fourth.
A clumsy three-putt from short of the fifth green cost McIlroy his first dropped shot of the day, but he quickly made amends with a birdie on the sixth.
A superb pitch on the par-five seventh set up another birdie and when he also picked up a shot on the ninth, McIlroy had covered the front nine in 31 to move inside the top 20 on four under.
Oosthuizen's record halfway total of 129 had given him a two-shot lead over 2020 US PGA champion Collin Morikawa, with 2017 Open winner Jordan Spieth a shot further back.
World number one Dustin Johnson was four shots off the pace alongside Scottie Scheffler and Dylan Frittelli, with England's Andy Sullivan leading the home challenge on six under.
Four-time major winner Brooks Koepka, who was eager to score more points in his spat with DeChambeau by pointing out he "loved" his driver after a 66 on Friday, was six off the lead on five under.