Alptekin, 27, ran the course in 4 minutes 5.11 seconds to win the first semifinal at the Olympic Stadium, finishing first among the 12 runners who took part in the race
Russia's Ekaterina Kostetskaya and Americans Morgan Uceny and Shannon Rowbury also qualified for Friday's final.
Gamze Bulut, 19, came in second in 4:01.18 in the other semifinal. The young athlete eased through the qualification with the fastest time of her career. Ethiopian Abeba Aregawi crossed the line first in 4:01.03. Russian Tatyana Tomashova finished the race in third place. The result has boosted morale of Turkish athletes in London amid frustrating performances in different sport fields.
Meanwhile, Karin Melis Mey of Turkey withdrew from the long jump qualifying round due to injury.