Wawrinka defeated the Finn 6-4, 6-2, 6-4, booking his place in the last 16 without dropping a set in the tournament so far.
Nieminen looked like giving the Swiss a challenge in the first set, until Wawrinka broke Nieminen's serve for the opening set.
Nieminen pushed hard again in the third set, and breaks were exchanged. However, when Nieminen was serving to stay in the match he had no answer when Wawrinka brought up three match points.
Wawrinka said: "I'm really happy with my game so far. I think today was a good match. It's been three really good matches. I think my game is there and I'm really happy to get through again."
Wawrinka will play either Spain's Guillermo Garcia-Lopez or Canadian Vasek Pospisil in the fourth round.