A semifinalist 12 months ago, McHale looked in store for another near-miss when she trailed Siniakova by a set and a break. However, a timely rain delay and a run of eight straight games turned the match on its head as the American closed out a 3-6, 6-4, 6-4 victory.
In a contest of numerous twists and turns, McHale was very nearly foiled at the last, Sinaikova rallying from 5-2 down to set up a tense conclusion.
Ultimately, McHale's nerve held steady, completing an emotional victory when Siniakova tugged a backhand wide.
"I don't even want to put my trophy down - i just want to hold it all the time," McHale said during the trophy presentation. "I've been coming to this tournament for a few years now and I really love it here. Thanks to all the fans and everyone here for sticking through all the rain delays - we've had a few, especially today!"
Sinaikova, who also lost in the Bastad final this summer, was unable to hide her disappointment at witnessing what would have been her first title slip away. "I'm here in the final for the second time and unfortunately it was really tough for me, so I'm a little sad. But Christina played really well, so congratulations to her," she said.
McHale, whose only previous WTA final came at Acapulco in 2014, endured a marathon journey to the winner's circle, spending over 13 hours on court after going the distance in each of her five matches.
For the first set and a half against Siniakova, this arduous route looked to have taken its toll. When the rain came, it halted the Czech just three games short of the trophy. Although, she held serve on the resumption, McHale sensed her chance going on the offensive to take the next three games and with it the set.
In the decider, McHale came out firing, a backhand onto the baseline helping her to a 2-0 lead. As her young opponent's frustrations boiled to the surface, she soon stretched this to 4-0. Siniakova rallied, reducing her arrears to 5-4 and threatening to stretch the match beyond the three-hour mark before McHale broke for a seventh and final time.
It was worth the wait ??. Thanks so much for an incredible week Tokyo and thanks for all the support!! pic.twitter.com/jIH1VvP2jX