The battle of the Aussies at the ATP Delray Beach Open on Wednesday has come to an abrupt end after Lleyton Hewitt was forced to withdraw from his match against Marinko Matosevic.
Matosevic won the first set against eighth seed Hewitt 7-6 before Hewitt retired with a right shoulder injury.
Hewitt had received treatment on the shoulder during the first set.
Matosevic will now play South Africa's Kevin Anderson in the quarter-finals.
The tournament's fourth seed has a 2-0 record against Matosevic, including beating him in the final of this tournament in 2012.
Meanwhile, US qualifier Steve Johnson, ranked 142nd in the world, stunned top seed Tommy Haas to reach the quarter-finals.
Johnson, a two-time US collegiate champion, dominated a third-set tiebreaker to beat world number 12 Haas 6-4 2-6 7-6 for his second career victory over a top-20 player.
Haas converted only three of his 12 break opportunities. Johnson, who saved all seven break points he faced in the opening set, pounced on Haas's miscues in the tiebreaker, when the German veteran double-faulted to fall 3-1 down, then sailed a backhand wide to give Johnson a commanding lead.
"In the third set, I kept my composure, didn't give him much and played a great 'breaker," said Johnson, who next faces sixth-seeded Spaniard Feliciano Lopez. "Tommy is an unbelievable player and this is a win I won't forget."
Lopez advanced with a 4-6 6-4 6-2 victory over France's Adrian Mannarino.
