Former US Open champion Juan Martin del Potro's comeback from a lengthy injury layoff was cut short by Kazakhstan qualifier Mikhail Kukushkin in the quarter-finals of the Sydney international.
The towering Argentine was out for 10 months after having surgery to fix an issue with his left wrist and went down 7-6, 7-6 to Kukushkin, ranked 66th in the world.
Defending champion Del Potro, who won the US Open in 2009, has seen his ranking plummet to 338 and had hoped to get some match practice in Sydney before the Australian Open begins in Melbourne from Monday.
There was not much to choose between the two players, who went unbroken throughout the match, barring a few points in the tiebreakers.
Kukushkin will take on fifth-seed Leonardo Mayer in the semi-finals after the Argentine defeated fourth-seed Julien Benneteau of France 6-3, 7-6.
Meanwhile, Wimbledon champion and second-seeded Petra Kvitova beat Tsvetana Pironkova of Bulgaria 7-5, 6-1 to advance to the women's singles final.
Kvitova will play Karolina Pliskova, who beat Germany's Angelique Kerber 6-3, 6-2.