After two hours and five minutes of tightly-contested play, the Swiss leads two sets to love, 7-6 (7-4), 7-6 (7-4) before poor light stopped play.
Thirteen aces from Wawrinka balanced a similar number of forehand errors, but, aggressive from the outset, testing his opponent's athleticism in every rally, his weightier shots seemed always slightly to have the edge.
He broke Dimitrov in the first game, but the Bulgarian broke back in the sixth and play remained finely balanced until the tie-break. "Ooh la la la la la," as one spectator called out. Wawrinka 1-3, turned it around to seal the first set.
The second set stayed on serve and had everything - aces, drop shots, fiery groundstroke winners, theatrical smashes, Mexican waves, a pigeon flying laps of honour above the net - until the second tie-break. Two aces and an unreturnable serve gave second set to Wawrinka, leaving Dimitrov, who did little wrong, retiring to sleep on a two-set deficit. Roll on tomorrow, when this match resumes on the court known - aptly for this contest - as the Bullring.
Meanwhile, Stefanos Tsitsipas and Filip Krajinovic were forced to match off Court Philippe-Chatrier at 9:52pm with the former just two games away from securing a three-set win over his Serbian opponent.
The sixth-seeded Tsitsipas, who is looking to make his first Roland-Garros fourth round, was leading Krajinovic 7-5, 6-3, 5-5 when their match was suspended for darkness.