Juan Martin del Potro says humid conditions played a major role in his three-set ASB Classic final loss to Roberto Bautista Agut.
The second-seeded del Potro - a red-hot favourite for Saturday's Auckland final - fell 1-6 6-4 5-7 to his Spanish opponent, failing to fire early on.
The ex-US Open winner and 2009 Classic champion was broken in each of his three first-set service games and didn't rebound until late in the second.
He secured the second set 6-4 but couldn't find a way past the consistent Bautista Agut in the decider, falling 5-7 and losing in just over two hours.
A star attraction at this year's Classic, the world No.12 del Potro was scheduled for night matches on each day and thus felt unprepared for his afternoon final.
It took him time to adjust to the heat and humidity.
"I was playing every match during the night and today was really hard, to play with this sun and humidity - I felt it a lot, in the start of the match. But then my game improved a little bit and I made mistakes in the last game," del Potro said.
"Roberto played solid in the last two games of the match, that was key.
"I didn't play another match during the day, so I felt a big difference in the weather, but it's not an excuse - I had my chances to win too."
The giant Argentine, who beat Denis Shapovalov, Karen Khachanov and David Ferrer on his way to the final, said he'd take nothing but positives from this week.
He'd now head to the Australian Open in high spirits.
"I played another final, I don't have anything to lose at this time of my career - I'm going to be top-10 again after big problems with my wrists," del Potro said.
"I have many good things to celebrate - of course, when you lose in a final, it's not happiness, but the tennis life continues."