Well done, Kei!
First victory at USO by a Japanese player since Shuzo Matsuoka in 1993.
Love his variety, change of pace and timing to approach the net.
Kei retired injured in Wimbledon, Pico had a back injury and didn't play Wimbers, he also suffered from pneumonia in July, losing a lot of weight. They both came back in the Olympics and lost in the first round.
Pico was clearly not back to form and making many uncharacteristic UEs although he fought back hard to take the tipsy turvy third set.
When Kei was serving at *3-2 40-0, he suddenly limped to the chair and called a trainer. He probably had cramps on both thighs and lower back. It took long for the trainer to come to Court 10, so maybe it helped Kei to recover quickly in addition to the on-court treatment he had.
Good luck vs Karanusic!