Two-time Grand Slam champion Angelique Kerber thrashed Madison Keys in just 51 minutes to reach the Australian Open semi-finals.

The 30-year-old German was in brilliant form as she beat American Keys 6-1 6-2 on Rod Laver Arena.

“It’s always tough to play against Madison,” said Kerber, who also won the US Open in 2016.

“She is hitting the ball so hard and I was just trying from the beginning, like I played the whole week, just to play my game.

The match was billed as a classic contrast of styles, the big-serving power game of Keys versus the scurrying, chase-everything-down, all-action approach of Kerber. For Keys so much depends on the serve, which is a formidable weapon.

When on song it sets up the American’s power game as in her last-16 match when she blew away Caroline Garcia with 32 winners on the back of nine aces.

But on Wednesday Kerber negated it from the off, winning 57 percent of points on Keys’ first serve.

And, without a plan B, Keys was broken four times in an error-riddled five games as the German raced to the first set 6-1 in 22 minutes and went 3-1 up in the second.

Keys, who reached the semi-finals at Melbourne in 2015, momentarily held back the tide with a break to love to get back to 3-2.

But the German juggernaut rolled on with a break back and a dominant hold, sealed with a tremendous overhead from near the baseline, to give Kerber a 5-2 advantage.

Keys, serving to stay in the tournament, opened with two double faults and moments later Kerber was back in the semi-finals where she will face either top seed Simona Halep or sixth seed Karolina Pliskova.

(with inputs from AFP)