With the family in tow, Ronaldo had prime seats to watch Novak Djokovic take on John Isner - the former ultimately trouncing the latter in straight sets to keep his quest for a record-equalling sixth Finals title on track.
World number one Djokovic, though, was playing a different game, appearing little troubled by the howitzers coming off the giant Isner's racquet - breaking his opponent three times and not conceding a single break point on his own serve.
"The match was great, obviously", said the 31-year-old.
Speaking about the court conditions, he said: "It takes a little bit of time really to get yourself adjusted to the surface.it takes a lot of rotation, takes a lot of spins. When you serve well, also it accelerates through the court".
Isner applied himself admirably but barely avoided being broken a few times in the first set, and was broken twice more in the second set.
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Djokovic, who replaced the injured Rafael Nadal at the top of the rankings last week, has stormed up the charts this year following elbow surgery and a period of indifferent form, winning Wimbledon and the US Open along the way.
The 30-year-old Cilic, who has a reputation for faltering under intense pressure, broke first but the German hit back, going on to edge the tie-break. Cilic drew first blood in the second game when he moved ahead after a deep return that Zverev failed to control, opening a 3-0 lead and creating two more break points in the fourth game for an even bigger lead.
There were a total of 78 unforced errors in the contest - with Australian Open finalist Cilic hitting 46 of those - as both players struggled to adapt to the court conditions.
"The court is hard", said Zverev. And it's very high-bouncing as well. Marin netted an easy forehand in the third point of the tie break to fall behind and he lost the focus completely, refusing to challenge some close calls from the line judges and giving Sascha five match points after a backhand down the line victor from the German in the seventh point.