Collins, who announced in January that she would retire from professional tennis at the end of this season, won 89.7% of her first serve points against Garcia, never faced a break point and converted three of her eight break-point chances.
The victory, sealed in a tidy 80 minutes, marked the first time Collins has won five consecutive matches on the WTA Tour since the 2022 Australian Open where she reached her first Grand Slam final.
Up next for Collins will be either fifth seeded compatriot Jessica Pegula (29) or Russian 14th seed Ekaterina Alexandrova (29).