Del Potro also finished past year strongly and the second seed saw off Denis Shapovalov 6-2 6-4 five days before the Australian Open begins, setting up a meeting with Karen Khachanov - who beat sixth seed Pablo Cuevas 6-2 7-6 (7-4).
Taking a 3-0 lead, he served his way to victory, banging 11 aces and nailing 73 per cent of his first serves against a valiant but imprecise Khachanov.
Four-time champion David Ferrer of Spain reached the semifinals of the ATP Tour's ASB Classic for the eighth time when he beat South Korea's Hyeon Chung 6-3, 6-2 in Thursday's quarterfinals.
Apart from Sock's departure, one of the main surprises Wednesday was the ease in which second-seeded Juan Martin del Potro dismissed Canadian teenage star Denis Shapovalov.
Del Potro's form in Auckland this week has been outstanding and he has shown no signs of a wrist injury which has dogged his career.
The 25-year-old Sock, the defending Classic champion, said he'd now look to reset for a grand-slam tilt in Melbourne, where he is considered a frontrunner.
Floyd Mayweather is clueless about "Me Too" movement
Floyd can't be serious, can he? "As a boxing fan - this is gonna sound unusual - I welcome it", Espinoza said. I've been saying ever since the first fight that there was a high chance these two would fight again.
"I'll be OK for tomorrow, I have enough time to recover now - in the final, no pain matters, so I'll have to be focused on the game".
In a battle between the 2016 and 2015 winners, the more recent champion Roberto Bautista Agut proved too good for Jiri Vesely with a 7-6, 7-2 victory to enter the semi-finals where he will play Robin Haase of the Netherlands on Friday.
Khachanov beat sixth seed Pablo Cuevas of Uruguay 6-2, 7-6 (4) to advance to the quarter-finals.
He cruised through a first-set tiebreaker after both players could not break serve, before seizing the initiative at the start of the second set.
"Today the conditions were hard and he was a hard opponent, serving very well and a lefty, playing with a very flat backhand", Bautista Agut said.