Kerber was able to handle the previously dangerous American serve with excellent returning, while holding her serve consistently, requiring no aces and being broken only once from just two break points created by Keys.
Angie is now back to her Australian Open winning touch and her semi final with Vika Azarenka should be riveting viewing.
Vika is the form player on the WTA Tour at present, and rightfully will start favourite for the semi final, seeking revenge for the quarter final loss to Angie in Melbourne, and aiming for the Indian Wells Miami double, achieved last by a female player in 2005 by Kim Clijsters and by only one other woman - Steffi Graf - in 1994 and 1996.
Vika, seeded 13 for this tournament, but guaranteed a ranking jump to at least five after she leaves Florida, emphasised the gap between the elite women in the sport and the improvers such as Britain's Johanna Konta. Konta has made giant strides this year, starting with the first Grand Slam title in Melbourne, but could not compete with Azarenka this time, losing out 4-6 2-6.
To be fair, the first set was fairly even, with just the one break of serve, and Konta having a number of chances. Vika just knew how to win the important points and after taking the first set she shifted up several gears which for the moment Johanna doesn't possess.
Azarenka doubled her success rate with points won on second serve, and won twice as many points as Konta for the set overall. A gentle approach to winning in set one suddenly became a desire to kill in straight sets, and that is what is likely to face Kerber.
Two men's quarter finals also were on display for the crowd, and Belgian David Goffin, seeded 15 met 18th seed Gilles Simon from France in the first of these. Fresh from pummelling Pouille in the round of 16, Simon was delighted to continue his latest hobby on Goffin in set one,
Despite a less than impressive 51% first serve success, and having to save six break points, Simon won enough of the rallies to confound most of the stats and win the most important one 6-3.
However, Goffin has had a habit of coming from behind in recent weeks to capture important wins and he didn't fail the test today, dominating Simon to win the final two sets 6-2 6-1, this time converting 5 of his six break points.
The other quarter final from the top half of the draw played out as predicted, and it was notably Novak Djokovic playing his best tennis for the tournament so far. Sadly for Tomas Berdych it had to be his quarter final in which the top seed decided to release some of his better shot making and artistry.
Leading into this clash, Djokovic had won the last 9 head to head, and 22 of 24 all time. Berdych had never won on hard court against Djokovic, so this would be a first. And of course it wasn't. 10 in a row and apart from a few glimpses of Berdych brilliance, it was direction predicable.
6-3 6-3, but the second set was more dominant. Djokovic created five break points on the Czech serve and broke twice - the Serb serve did not face a single break chance.
The Djokovic first serve percentage rose from 57 to 75 set one to set two. He won all points on his second serve in set two.
Overall in set two the world number one won about 80% of points while serving, compared with Berdych 50% on his booming delivery. This is the kind of returning of serve with which Goffin will need to deal, should he be entertaining thoughts of a final appearance.
Tomorrow sees the other two men's quarters - Nishikori v Monfils (my guess the steadier Nishikori to win) and Raonic v Kyrgios (Raonic firepower an edge heavier and should prevail)
The women's semis are also scheduled on a huge card and I think Timea Bacsinszky may outgun Sveta Kuznetsova, while Vika Azarenka is unstoppable and will win a great three setter against Angie Kerber.