Nick Kyrgios
Tennis - China Open - Men's Singles Finals - Beijing, China - October 8, 2017 - Nick Kyrgios of Australia sits on the bench during a change of ends as he plays against Rafael Nadal of Spain. Reuters / Thomas Peter

Australian World No. 1 Nick Kyrgios suffered an untimely elbow injury on Sunday during his straight-sets loss to German counterpart Alexander Zverev in the opening round of the 2018 Davis Cup. After the loss, Kyrgios was adamant he could not put forward his "best performance" against Zverev, ranked No. 5 in the world.

After the nations draw level on Day 1 of their 2018 Davis Cup clash at the Pat Rafter Arena in Brisbane, the German duo of Peter Gojowczyk and Tim Puetz survived a five-set marathon against Australian tandem Matthew Ebden and John Peers during a doubles contest on Saturday. The 6-4, 6-7, 6-2, 6-7, 6-4 victory in Rubber No. 3 gave Germany a 2-1 lead heading into the critical Kyrgios vs Zverev clash on Sunday.

If Kyrgios had defeated Zverev, there would have been another singles match (Rubber No. 5) between Jan-Lennard Struff and Alex de Minaur on Sunday. However, Zverev handed Kyrgios a 2-6, 6-7, 2-6 straight sets loss to send the Aussies packing.

After the loss, Kyrgios insisted that a shoulder injury left him compromised. "It's tough to go out and not be able to put in your best performance. It sucks. I had one eye on this Davis Cup tie throughout the whole Aussie summer. I was waiting to come here and play. It just leaves a bit of a bitter taste in my mouth after the Aussie summer I had. I can't really be too happy with the way I played or the result today at all. I would have given up my Brisbane title to have won this tie. Ultimately, I had a pretty good summer. But it's hard to think about all that stuff when I lost today," said Kyrgios, ranked No. 14 in the latest ATP Rankings.

Nick Kyrgios unable to end Aussie summer on high

After winning the Brisbane International, Kyrgios put forward an impressive showing at the 2018 Australian Open before a fourth-round loss to World No. 4 Grigor Dimitrov. The 22-year-old Canberran was hoping to cap off the Australian summer by guiding his country to the Davis Cup quarter-finals.

"I felt it the day after I played my first match. I didn't really think too much of it. I'm going to take a week off now to try and get it better. It affected me a fair bit in my match. My serve is my biggest strength. He (Zverev) played great... he served well. But my biggest weapon was not really there and that affects the rest of my game," Kyrgios added.

A first-round defeat is a disappointing outcome for Team Australia, a year after pushing Belgium to the brink in the 2017 Davis Cup semi-final. Lleyton Hewitt's team will now face a play in September to try and remain in the World Cup. Meanwhile, Germany will now progress to the Davis Cup 2018 quarterfinals.