Kiprop was forced to dip into his reserve on the home stretch and squeezed into the team with third place in a time of three minutes 38.30 seconds behind world silver medallist Silas Kiplagat (3:37.60) and Nixon Chepseba (3:38.00).
"I was blocked by runners who could not move, hence the delay in breaking through. However, I have learnt my lesson and will strategise for the Olympics well," Kiprop said.
Women's Olympic 1,500 champion Nancy Jebet Lagat will not defend her title in London after skipping the east African nation's final trials.
Jebet Lagat had said earlier in the week: "I have decided to take a break this year and I cannot confirm whether I will take part in the trials."
World indoor 3,000 champion Hellen Obiri took advantage of Jebet Lagat's absence to win the 1,500 in 4:06.10.
Double world champion Vivian Cheruiyot confirmed her place in the team for the 5,000 With a victory in 16:08.08 after winning the 10,000 last week.
She and Sally Kipyego, who finished second in the 5,000, will double at the Olympics.
Olympic men's 3,000 metres steeplechase champion Brimin Kipruto beat world gold medallist Ezekiel Kemboi to the finish line.
Pamela Jelimo, who won Olympic gold in Beijing four years ago, led the 800 metres from the bell to beat 2007 world champion Janeth Jepkosgei.
Former world champion Eliud Kipchoge could only manage seventh in the men's 5,000 which was won by Isaiah Kiplangat in 13:09.80.