Frank de Boer's men suffered a shock defeat to the hosts, who hit the visitors hard in the second half with goals from Eric Botteghin and Michael de Leeuw
It is only the second occasion that coach Frank de Boer has lost back-to-back Eredivisie matches during his reign in Amsterdam. Not since early 2012, when losing to Feyenoord and Utrecht, had Ajax lost successive league games.
And certainly few would have thought Groningen - with only one win in 10 matches against today’s opponents - capable of creating a small piece of history against Ajax, chasing a fifth successive domestic title.
However, two goals in the second half from Eric Botteghin and Michael de Leeuw created this shock result which, coupled to the departure of Daley Blind, means it hasn't been the best of weeks for de Boer and Co.
Both sides lined up with identical records having played three games and with their one defeat apiece this season having come last weekend.
The biggest difference in the Ajax starting XI from the side beaten by PSV was the void left by Manchester United-bound Blind, his place going to the South African Thulani Serero.
Whether it was Blind’s absence or a hangover from that 3-1 loss to PSV, it took a while for Ajax to settle.
Indeed, neither side were particularly threatening in the opening half hour. It was, however, the champions who began to press Groningen and Ricardo van Rhijn should have done better when he overlapped down the right, deciding shoot when there were four Ajax shirts to aim for in the penalty area.
The chances kept dropping to Ajax and Sergio Padt saved well at point blank range from Davy Klaasen after the home defence has delayed clearing the danger, while the Groningen goalkeeper was relieved to see Nick Viergever’s dipping attempt from distance spin narrowly wide.
A blunder from Johan Kappelhof almost let Anwar El Ghazi in, but he skied his shot when looking for his third goal in as many games. As the half closed however, Groningen began to assert some pressure on the Ajax goal, without testing Jasper Cillessen fully.
That all changed into the second half. Ajax were slow out of the blocks and were punished for that lack of urgency when Nick van der Velden played Tjaronn Chery in on the left-side of the box, his low centre turned past Cillessen by Groningen central defender Botteghin, who had remained in an advance position from an earlier corner.
Groningen limited Ajax to some desperate long-range shooting, although Boilesen and substitute Ricardo Kishna with a free kick saved by Padt, came closest.
As time began to run out for Ajax, Groningen coach Erwin van de Looi’s optimism grew, and decided to utilise substitute Michael de Leeuw who had netted in the opening two games of the season after coming off the bench.
Three minutes from time, Chery produced another telling cross from the left, connecting with De Leeuw at the back post, and his powerful downward header beating Cillessen to hand the hosts all three points.