Lleyton Hewitt holds key to Davis Cup tie in Bernard Tomic's head

— -- two opening singles matches was as stark as the weather change that stormed through Kooyong only minutes after Tomic had levelled the tie.

If the combatants changed rackets for boxing gloves, Groth and Isner were the brutal heavyweights, going toe-to-toe trying to land quick knockout punches. Tomic and Sock, meanwhile, were light-footed welterweights, dancing around the court, swinging dazzling combinations before retreating, planning their next attack.

Tomic eventually won convincingly on points - his first in four attempts against Sock.

But for the home team to win the tie and progress to the quarterfinals, Tomic will surely have to break another duck - against Isner, who defeated the Australian in their only previous contest.

How Tomic's guile and court craft - and mindset - shape up against the incredible power of the American could decide this tie between the Davis Cup's two proudest nations.