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Just after Rafa Nadal subjected Australian number one Alex de Minaur to a straight sets humbling, second seed Kerber pounded into Birrell like a freight train and sent the 240th-ranked 20-year-old packing after 58 scarring minutes.
Shell-shocked under the lights in front of a packed centre court crowd, Birrell simply had nowhere to hide as the former world number one celebrated her 31st birthday by pummelling her opponent.
Kerber has enjoyed a birthday serenade from friendly Melbourne crowds for a number of years, but after seeing Birrell eviscerated, the terraces were hardly in full voice.
The German was unconcerned by the crowd's heartbreak.
"If you are there, you are professional," she told reporters.
"You are trying to play your match, trying to focus on the tennis, on the way how you would like to play, and on winning the matches. I'm not thinking about something like this."
German Kerber has enjoyed a rollicking start at the year's first Grand Slam and has an excellent chance to reach her third quarter-final in Melbourne after claiming the 2016 title and reaching the semi-finals last year.
She will play unseeded American Danielle Collins for a place in the last eight where former U.S. Open champion Sloane Stephens might wait should the draw go with seedings.
"I think it will be another good match ... I know her (Collins) a little bit. We played once I think last year.
"She hits the ball really hard and fast.
"It's another match that I know that I have to take it in my hand, playing my game."
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