Champion at the event in Washington DC in 2019 – his most recent ATP Tour title – Kyrgios somehow found the energy to get past Ymer, despite not sleeping until 5am local time as a result of having to play – and win – two matches on Saturday (AEST)
"Honestly I didn't play anywhere near my best tennis today and I don't know. The role was reversed, the past couple matches I've been on paper, rankings-wise the underdog in my past couple matches, but today I definitely felt like the favourite," Kyrgios said after the semi-final win.
"I served pretty solid. Obviously my winning percentage behind my first serve would have been high, but from the back of the court I didn't play well at all."
Kyrgios saved five match points in the second of of his two matches on Saturday (AEST) – a quarter-final against Frances Tiafoe – but he didn't have his back up against the wall against Ymer, although he did have to deal with the Swede's exceptional pace.
Ymer, who ousted former World No.1 Andy Murray in the first round, used his speed and defensive skills to great effect throughout the week and did so again against Kyrgios, finding small openings with sublime backhand passing shots.
But the match was on Kyrgios’s racquet, and the 27-year-old relied on his big serving and baseline power in key moments to triumph after one hour and 35 minutes. He was not at his flying best, showing consistent frustration throughout the first set, but his serve kept him out of danger as he did not face a break point.
Kyrgios did not hit 35 aces like he did against Tiafoe, striking 10, but it was good enough for the victory.
"The difference was he stands on the fast and he makes you play that extra ball. He's an incredible athlete and I really wasn't expecting him to be that fast," Kyrgios said. "Maybe next time I might have a couple different tactics when I play him, maybe not to try and out rally him, maybe come forward a little bit more. But it was a tough-fought semi-final and I'm just happy to be in the final once again."
The first set could have gone either way, with the pair tied at 4-4 in the first-set tie-break. In an uncharacteristic Kyrgios rally, which featured plenty of slices between the two, the Australian prevailed after 24 shots to seize the mini break and eventually, the set.
Kyrgios struggled to break through on Ymer's serve until 4-3 in the second set, when he finally earned the match's only break by flicking a forehand half volley from no-man's land crosscourt and out of the reach of the lunging Swede.
The World No.63 is up to No.42 in the ATP Live Rankings. If Kyrgios lifts the trophy, he will climb to No.37. He will play either Andrey Rublev of Yoshihita Nishioka in the final.