Nick Kyrgios left his girlfriend, Costeen Hatzi, blushing after his win over world number one Daniil Medvedev at the US Open on Sunday night. The Australian bad boy credited his 22-year-old partner for his improved form in the second half of the season.

The 27-year-old has been in fine form since the end of the French Open, with no player winning more matches on the ATP Tour. Kyrgios made the final at Wimbledon, won the Citi Open, and is now in his first quarterfinals at Flushing Meadows after a four-set win over Medvedev.

Kyrgios' talent was never in doubt, but it was his on-court temperament that has prevented him from winning big titles during his career. The Australian has proven to be consistent in recent months, making the latter stages at a number of events since the start of the grass court season.

Nick Kyrgios
Nick Kyrgios reacts during his victory over defending champion Daniil Medvedev at the US Open GETTY IMAGES NORTH AMERICA via AFP / Sarah Stier

After his win over Medvedev, the Australian was asked when it clicked "in the Kyrgios head." While the 27-year-old was unsure, he was quick to credit his girlfriend for keeping him more grounded and at home, while also thanking his entire team.

"I'm trying to work hard every day, make every session count. Before I would be out every night, now I have a great girlfriend, she helps me, she... you know," Kyrgios said with a coy smile as the camera panned to show Hatzi.

"And my team, I've got my physio with me, Will. My team, it's all my team and I'm just really happy and I'm hoping I can keep it going," he added. "I don't want to let them down, I've been on the road for four months, we all have families we want to see, I want to make this count."

Kyrgios' next opponent is Russian Karen Khachanov, who beat 12th seed Pablo Carreno Busta in a pulsating five set match that lasted three hours and 20 minutes. The Australian has no plans of stopping at the quarterfinals and wants to go all the way in New York.

"I want to go all the way. Hopefully it is possible." Kyrgios said. "I was just having a lot of fun, embracing every moment out on Ashe today. Really proud of that."

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Nick Kyrgios
'Never thought I'd make Slam final': Nick Kyrgios AFP / SEBASTIEN BOZON
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