The 29-year-old del Potro, an ex-US Open champion and the 2009 Classic victor, will face another ex-champion in Ferrer.
The 29-year-old second seed, who won the Auckland tournament the last time he played in it in 2009, will now return to the top 10 in the ATP rankings on Monday for the first time since August 2014 after struggling with injuries over the past few years.
In Sydney, 18-year-old Alex de Minaur continued to delight the home crowd with a 6-4 6-4 win against Feliciano Lopez and will face Benoit Paire in the semi-finals, after the Frenchman knocked out defending champion Gilles Muller.
In what proved a sterner test than his first-up victory against equally youthful Denis Shapovalov, del Potro on Thursday dominated all of the key moments to win 7-6 (7-4) 6-3.
Argentina's del Potro, who beat Querrey to win the 2009 ASB Classic, needed only an hour to beat Shapovalov 6-2, 6-4.
"I served really well in the second set and I tried to play aggressively".