Gauff has spent 9hr 19min on court in singles so far this fortnight, and another four and a half hours across doubles and mixed doubles (she is through to the doubles quarter-finals alongside Jessica Pegula).
“I just feel so fresh, to be honest. I don't know if it's because I've been tricking myself or maybe when this is over I'm going to hit a wall. But I'm really proud of how I'm able to get through these matches,” added Gauff.
The 19-year-old needed just 68 minutes on Tuesday to dismiss Ostapenko, whose level was nowhere close to how she played during her three-set victory over world No.1 Iga Swiatek on Sunday night.
The Latvian former Roland-Garros champion landed just 38 percent of her first serves in, and committed 36 unforced errors against 12 winners.
“Today was not really good match from me. I think it's really hard to recover from those night matches, because after beating world No.1, I went to sleep at, like, 5:00 in the morning, and still, you sleep for, I don't know, maybe like seven, eight hours, but you completely don't recover,” said the 20th-seeded Ostapenko.
“Yesterday the whole day I felt very low energy. I thought today I was going to wake up and feel better. But honestly, I didn't really feel much better.”