The top seed needed just 59 minutes to see off the challenge of Lu, breaking the man from Taiwan on five occasions as he registered a 6-1, 6-3 victory.
Nishikori will face fifth seed Alexandr Dolgopolov in the last eight after the Ukrainian saw off Austrian Andreas Haider-Maurer with a 6-2, 6-3.
Defending champion Grigor Dimitrov saw his defence end in the second round as he went down 7-5, 4-6, 6-0 to American qualifier Ryan Harrison.
On his 23rd attempt the 22-year-old Harrison finally managed to beat a top ten player, and he did so with ease in the end.
After two tight sets were split between the pair, Harrison was able to step it up in the decider and broke Dimitrov three times, with the third seed managing just eleven points in the set.
Harrison will face Ivo Karlovic, last week's winner in Delray Beach, after the Croatian recovered from a slow start to beat Dusan Lajovic 3-6, 6-3, 6-1.
Fourth seed Kevin Anderson was another who needed three sets to secure his progression. The South African faced a tough battle against Steve Johnson, but was eventually able to subdue the American with a 3-6, 7-5, 6-3 win.
There were also wins for Viktor Troicki and Bernard Tomic.