The desire to start Lleyton Hewitt’s Davis Cup captaincy off with a win drove Australian No.1 Bernard Tomic to a gutsy victory on Friday over American Jack Sock.

Tomic endured a rollercoaster match in their World Group first-round tie at Kooyong and came out on top 7-6 (7-2) 6-3 3-6 6-4.

After Sam Groth earlier fell to US No.1 John Isner 7-6 (7-2) 6-2 6-2 and, with champions Mike and Bob Bryan lining up for the American in the doubles on Saturday, the pressure was on Tomic.

He looked comfortable in the first two sets but lost his way in the searing heat on the temporary grasscourt.

Cheered on by Hewitt, who took over as captain this year, Tomic lifted to break Sock at 4-4 in the fourth set and then served out the match.

Tomic said it was one of the most-satisfying wins of his career, having never beaten world No.24 Sock – and with so much at stake.

He admitted he had a lapse in concentration in the third set but Hewitt helped get him back on track.

“I was losing a lot of games very comfortably on Jack’s serve and Lleyton was encouraging me and saying the right things,” Tomic said.

“It was an amazing situation to be a part of; the first time that Lleyton was in the chair for me and it really was a great honour.”

Hewitt praised Tomic, who only arrived in Australia from Mexico earlier this week and had to adjust to the grass.

“It’s not an easy thing to do, to come out when you’re the No.1 player and you’re one-love down in Davis Cup but Bernie did fantastic today,” Hewitt said.

USA team captain Jim Courier said despite the 1-1 scoreline after day one, he felt like his team had an edge with the Bryan brothers on board.

The Americans are striving for their first victory over Australia since 1997 while they haven’t won here since 1982.

The Bryans have won 16 grand slam doubles titles and have an imposing 23-4 Davis Cup win-loss record. Australia’s combination of Groth and debutant John Peers have only played one tournament together.

“Bob and Mike Bryan seem to be an advantage in the historical candour of doubles in Davis Cup,” Courier said.

“They’ve played awfully well and we feel confident in them but they’ve lost matches too so we don’t take anything for granted but I love having them on our side.”

Hewitt replaced an ill Nick Kyrgios in the four-man team and could yet substitute to play doubles with Peers.

He said he hadn’t spoken to his team about it yet.