Both men helped deliver an exhilarating match with the Austrian emerging victorious from the high-quality affair after winning two tiebreakers — 7-6 (9-7) 7-6 (7-4).
It’s just a shame no fans were in the arena to witness the encounter, with matches being played behind closed doors at the O2 Arena in London amid the pandemic.
Those watching from home were treated to a true spectacle though — the opening set alone lasted one hour and 12 minutes with both men making just 19 unforced errors between them.
“It was a great match from the first to the last point. I was pretty lucky to get the first set,” Thiem said after the match.
“I knew I had a slight advantage when I won the first set but I had to stay super focused. The atmosphere would have been unreal today I guess, but I hope that we put a very good show on for all the people who watched on TV.
“It’s very tough times at the moment, strict lockdowns in most of the countries as well as in Austria since today.
“So I really hope people enjoyed the match back home and they forgot a little bit for two hours, 30 minutes the tough times we’re living through right now.”
As of November 17, Austria is entering stricter lockdown measures with people only allowed to leave their homes for a specific reason, such as going to work, shopping for basic goods, and for medical appointments.
Bars, pubs and restaurants are now closed along with schools, with teaching being done remotely.
The new measures are scheduled to run until December 6, says the interior ministry.
Thiem faced two set points in an intense opening set which saw both men push each other to their very best tennis.
It was the Austrian who held his nerve in the tiebreaker though, slapping a wonderful forehand across the court to take the lead in the match.
Nadal, who brushed aside Andrey Rublev 6-3 6-4 in his opening match, could barely have played better and the levels didn’t drop at the start of an extraordinary second set.
The Spaniard’s form did temporarily abandon him when serving to stay in the match though, after he made three uncharacteristic mistakes which handed Thiem three match points.
However, the 20-time grand slam champion pulled off a stunning escape to stay in the encounter and eventually force a tiebreak, with Thiem once again edging it.
“I think it’s important that we players who are privileged to do our job, give all the people who are not that privileged a great time,” Thiem added.
The reigning US Open champion progresses to the semifinals of the tournament with one game to spare after Stefanos Tsitsipas beat Rublev 6-1 4-6 7-6 (8-6) later on Tuesday.
Tsitsipas won last year’s edition but had to dip deep to get past his Russian opponent. The 22-year-old faced match point in the third-set tiebreak but recovered to claim victory.
Nadal, who has never won the ATP Finals, will face Tsitsipas in his next match, with the winner progressing to the knockout stages.