"I didn't really imagine being back", a teary Kvitova said after defeating No. 15 Ash Barty of Australia 6-1, 6-4.
"I'm just living the dream, living what I've been working hard for", Tsitsipas added.
There was no argument from the 37-year-old, however, and he stopped and waited patiently for his entourage to catch up with him. When I was answering that question I thought I was insane. But it is real.
Nadal, 32, has been in top form, winning every set he's played in the tournament so far - the first time he's done so en route to the semifinals since 2009, the only time he's won the first Grand Slam of the season.
And, despite not playing competitively since September's US Open because of multiple injuries, he has cruised through his opening five matches.
After encountering the gifted Greek at close quarters for the first time he still tipped either Nadal or Novak Djokovic to lift the famous Norman Brookes trophy.
"It was a good quality of tennis in that first set".
And while it was not three hours of sustained brilliance against Bautista Agut, Tsitsipas hit some incredible highs. "I think he knows the game".
He had spent nearly 12 hours on court coming into the match - more than three hours longer than Nadal - including his four-set wins over Wimbledon finalist Kevin Anderson and former world number four Grigor Dimitrov.
Meanwhile, Canada's Gabriela Dabrowski reached the mixed doubles semifinals with a 6-4, 6-3 victory.
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Bautista Agut, victor at the Qatar Open earlier this month, regained his composure to secure an early break in the second set, and deservedly levelled the match as Tsitsipas' concentration levels dropped.
Dabrowski and partner Mete Pavic won their second round match 6-4, 6-3 and advanced to the quarter-finals.
And when another break followed the Athenian artist had his nose back in front and the Spaniard could see the match slipping away.
"I knew he was going to bring insane intensity, I knew the ball was going to be jumping", said Tiafoe. What do you want me to tell you?' he laughed when speaking to Eurosport following his win.
Having never previously progressed beyond the fourth round at a major, an emotional Tsitsipas was lost for words after prevailing in a fourth-set tiebreaker.
As Nadal served at 5-4, Berdych complained to the umpire about the finicky Spaniard being too slow between points.
He then showed incredible resilience at 5-6, 30-40 to repel a first match point after a 21-shot baseline rally.
He double-faulted to give Tsitsipas a match point at 6-5 but saved it with a fearless forehand down the line and repeated the feat to send the set into a tiebreaker.