King served seven aces in the match, but Lu won 75 percent of his service points and advanced to a meeting with Denis Istomin, who polished off Lukas Lako 6-1, 6-3 earlier in the day.
Other winners Tuesday included Ricardas Berankis of Lithuania and Santiago Giraldo of Colombia.
Sixth-seeded Mardy Fish of the United States was trailing fellow American Michael Russell when rain brought Tuesday's play to a premature close. Russell won the first set 6-4, but Fish was ahead 2-4 in the second when play was called. The match will be decided Wednesday along with the postponed tilt between Tim Smyczek and James Blake.
Swim Week Miami Beach 2014 [PHOTOS]