Sinner into US Open quarter-finals
The 11th seed squeezed past the 28-year-old Belarusian 6-1, 5-7, 6-2, 4-6, 6-3 to set up last eight meeting with either Spain's Carlos Alcaraz or Croatia's Marin Cilic on Wednesday.
The Monaco-based 21-year-old has performed consistently well at Grand Slams this year, reaching quarter-finals at the Australian Open and Wimbledon, and the fourth round at the French Open.
Sinner struggled to find consistency during his 3hr 48min tussle with Ivashka on the Louis Armstrong Stadium court.
The Italian served up 14 double faults and made 55 unforced errors during a patchy display.
Ivashka failed to capitalise on Sinner's erratic performance, with 13 double faults of his own and 64 unforced errors.