Roger Federer brushed past Philipp Kohlschreiber to set up a blockbuster US Open quarter-final against Juan Martin del Potro.
Federer improved to 12-0 head-to-head against the German thanks to a 6-4 6-2 7-5 fourth-round victory on Arthur Ashe Stadium on Monday.
However, the Swiss third seed did take a medical timeout off court at the end of the second set.
The 19-time grand slam champion was seemingly troubled by his back again, but he showed few signs of injury during a 109-minute win.
Into a 12th quarter-final in New York, Federer produced a fine performance against Kohlschreiber, setting up a clash against Del Potro in a repeat of the 2009 decider and moving a step closer to a last-four meeting with Rafael Nadal.
It continued a friendly run into the last eight for Federer, who has now beaten three players against whom he holds perfect records – Mikhail Youzhny (now 17-0), Feliciano Lopez (13-0) and Kohlschreiber (12-0).
Kohlschreiber matched it with Federer early, only to give up a 40-0 lead and be broken in the seventh game when the Swiss star hit a forehand winner.
That allowed Federer to take control, two more breaks – and losing just four points on serve – seeing him through the second set.
Unusually, the 36-year-old took a medical timeout before the third set, but he broke in the 11th game thanks to a backhand winner on his way to a straightforward victory.
Federer  bt Kohlschreiber  6-4 6-2 7-5
Federer - 39/20
Kohlschreiber - 19/33
Federer - 11/2
Kohlschreiber - 4/2
BREAK POINTS WON
Federer - 4/7
Kohlschreiber - 0/0
FIRST SERVE PERCENTAGE
Federer - 65
Kohlschreiber - 57
PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE
Federer - 88/73
Kohlschreiber - 67/49
Federer - 101
Kohlschreiber - 70