Team USA's Sam Watson climbed up the wall in 4.75 seconds, 0.04 seconds faster than the world record previously set by him in April.
Veddriq Leonardo from Indonesia came second, clocking 4.79 seconds and Kazakhstan’s Amir Maimuratov finished in third place with 4.89 seconds.
Alipour advanced to the final with a run time of 5.06 seconds as the fastest elimination heat loser.
The top eight men advance to the final on August 8.
Men's speed semifinal (Top 8):
Sam Watson (USA): 4.75 seconds (WR)
Veddriq Leonardo (INA): 4.79 seconds
Amir Maimuratov (KAZ): 4.89 seconds
Matteo Zurloni (ITA): 4.94 seconds
Wu Peng (CHN): 5.00 seconds
Reza Alipour (IRI): 5.06 seconds
Bassa Mawem (FRA): 5.16 seconds
Julian David (NZL): 5.20 seconds