Sam Burns found himself behind early on against Young but responded brilliantly, winning four holes in a row from the fifth to turn the match on its head at Austin Country Club.
Defending champion Scottie Scheffler maintained his phenomenal record at this event - where he has finished second and first in the last two editions - with a three-hole victory over Tom Kim. World Number Three McIlroy beat Keegan Bradley in a repeat of their 2012 Ryder Cup singles clash.
Kim, a four-time PGA Tour winner, swept to a 4 and 3 victory over World No. 9 Viktor Hovland in his Group 8 match at Austin Country Club and needs only a tie in his final group match to advance out of the group stage