The fifth-seeded Nishikori advanced to the finals of the U.S. National Indoor Tennis Championships in a walkover when Australian Marinko Matosevic retired with a foot injury after the Japanese took the first set 6-4.
Nishikori will be seeking his third ATP Tour title in five finals appearances Sunday.
He'll be facing Lopez, who went three sets to get past Uzbekistan's Denis Istomin 6-2, 3-6, 6-3.
Lopez will also be seeking his third career crown and first since 2010.
Notable deaths of 2014 [PHOTOS]