The panic at losing the first set – prolonging the game to 2hr 29 mins – was nothing compared to being woken up at 4am in the morning thinking there was a fire.
“It’s been an interesting morning so far. The fire alarm went off in our hotel at 4am this morning,” Sock revealed courtside.
“I love playing in London. You make me feel at home. My coach nicknamed me Showtime when I was young because I always love to play in front of people. There’s always a lot going on. I don’t even know what I’m doing some times.”
It was a stunning finale, but in truth the show had taken a little while to get going.
The tournament had received a massive blow the night before with the withdrawal of world No.1 Rafa Nadal – the Spaniard deciding it was time to succumb formally to his knee injury following his defeat to David Goffin of Belgium.
It meant the atmosphere was still a bit muted at the O2 in the early afternoon as Cilic and Sock, very much the undercard to tonight’s Roger Federer versus Alexander Zverev battle of the generations, took to court.
And in a surprisingly lacklustre start by both men, breaks of serve were traded in a nervy outset before the bang-crash encounter chugged along in more predictable fashion.
Cilic had lost his two previous encounters against the American, but with Sock needing to hold serve to take the first set to a tie-break, he suddenly found himself 0-40 down as Cilic moved his game up through the gears. Gamely, Sock saved the first two set points but when he slapped a loose shot into the net on the third, it was first blood Croatia. Cilic punched the air.
Sock had showed in his opening encounter with Federer – including a between-the-legs volley and a bottom-wiggling incident – that he is here in London determined to make an impression.
Breaking at the first opportunity in the second set with a well-disguised lob, and with Cilic helping him along with four double faults and a wild forehand that missed even the tramlines to give Sock a second break.
The 25-year-old was trying to mix things up more – the occasional deft drop shot punctuating the power-struggle.
However, it was Cilic who got the early break in the third set but, undeterred, Sock broke back and this time we were into a tie-break – the cold war finally reached critical point.
Neither side was prepared to back down – Sock scampering to retrieve a net cord shot from Cilic to the delight of a packed crowd that was by now on its feet.
The momentum took him a mini-break up and the battle seemed to have fallen out of Cilic. A final loose backhand long and a fiercely American fist-pump marked Sock’s first ever victory in these finals. Another on Thursday will almost certainly put him in the semi-finals.