KOOYONG -- Australia's first-round World Group Davis Cup tie against the U..S is balanced on a knife edge after a see-sawing, sweltering day at Melbourne's historic Kooyong.
After world No. 11 John Isner overpowered Australia's Sam Groth, Bernard Tomic ensured the home team shared the honours on the first day of the three-day tie by edging past Jack Sock. Tomic has forged an imposing Davis Cup singles record -- it now sits at 16-3 -- and his 7-6(2), 6-3, 3-6, 6-4 victory was vital for the home team, which was already weakened by the loss of Nick Kyrgios.
Aside from a third-set slump, Tomic was masterful in trying conditions against Sock, ranked four places lower than his Australian opponent at No. 24 in the world.
The Australian was cruising at two sets up but a dramatic turnaround allowed the American back into the contest. A suddenly lethargic Tomic dropped the third set but recovered in the fourth, ensuring the tie between the two most decorated teams in Davis Cup history was split at 1-1 on Friday.
Tomic paid tribute to first-time Australian captain Lleyton Hewitt after his win.
"Having Lleyton there by my side means a lot to me," Tomic said. "I had to come into this match focused."
Earlier, Isner had given the U.S. a perfect start. The monster-serving world No.11 wore down his 77th-ranked opponent after a titanic first set, powering away to win 7-6(2) 6-2 6-2 in one hour and 48 minutes.
With an unexpected heatwave pushing temperatures past 30C, Isner showcased the power, skill and temperament that have pushed him back to the brink of the world's top 10.
He survived a fierce first-set examination from a pumped-up Groth, who had the home crowd roaring several times in an explosive opening.
But the American had all the answers in the tiebreak, lifting a gear against the Australian and carrying the momentum through the second and third sets as Groth's challenge wilted; Isner's 20 aces and 67 per cent first-service percentage proving too strong.
One team will gain a decisive advantage after the crucial doubles contest, with Groth set to partner the unheralded John Peers against the intimidating Bryan brothers, Mike and Bob. However, teams can change players up to an hour before play, and Australia may yet play Hewitt.
The tie will conclude after Sunday's reverse singles.
The U.S. has not defeated Australia on their own soil since 1982, when John McEnroe led his team to a decisive win in the World Group semifinals. It is the countries' 46th meeting, with the U.S. leading the head-to-head 25-20. They haven't clashed since 1999, when Hewitt and Pat Rafter led Australia to a 4-1 victory over an American team featuring Jim Courier - now the U.S. captain.