"I'm so relieved to go through," the 50-year-old told Japanese media on Friday after Japan lost 2-1 on the night but squeezed past Kuwait 4-3 on aggregate.
Goals from Hamad Aman and Yousef Nasser gave Kuwait victory in Thursday's second leg but Japan held on to win despite a fierce late barrage from the home side.
"The players gritted their teeth and got the job done," said Sekizuka, whose side are bidding to qualify for a fifth successive Olympics in London next year.
"That was a punishing experience but the players kept battling. Regardless of the performance I'm proud of them for how they fought and coped with the heat."
With temperatures nudging 40 degrees Celsius at kickoff, Japan ultimately wriggled through courtesy of Hiroki Sakai's superb 21st-minute chip, which opened the scoring.
Japan, who beat Kuwait 3-1 in the home leg, were also grateful for a heart-stopping late save by goalkeeper Shuichi Gondo which prevented the game going to extra-time.
"Kuwait came at us guns blazing but 20 minutes into the second half, I thought we had more left in the tank than them," claimed Sekizuka, at ease having been saved the stress of an extra 30 minutes.
The final round of Asian qualifiers for the 2012 Olympics begins in September, involving the region's top 12 sides.
