A youthful Ospreys line-up went down fighting in an entertaining contest at the foot of the Pyrenees.
The Ospreys were forced into a late change ahead of kick-off when Keelan Giles tweaked his hamstring during the warm-up, Hanno Dirksen coming into the starting XV with Tom Williams taking the number 23 jersey.
It was the visitors who enjoyed the better of the early exchanges but they were unable to take full advantage of their possession as the lineout misfired on several occasions.
However,it was Pau who opened the scoring just before the half hour mark.
An offside in midfield allowed Antoine Hastoy to go to the corner and as Pau pressed with a penalty advantage in their favour, good work saw them create an overlap on the right, good hands making it an easy finish for Vincent Pinto, who was hugging the touchline.
The conversion from Hastoy was good and Pau were soon back on the attack. Charley Malie and Benson Stanley combined well up the left and it looked like a certain try only for Watisoni Votu to lose the ball forward in the tackle as he attempts to get it down
Back came the visitors, attacking from a line out on the left, Gareth Thomas made a powerful run to carry close to the line where Pau offended and a yellow card was shown to flanker Baptiste Pesenti two minutes from the break.
HALF-TIME: PAU 7-0 OSPREYS
With an extra man it was crucial that the Ospreys started positively, and they stuck twice inside the first nine minutes of the second half to take the lead.
From a line out on the right Harri Morgan fed Tiaan Thomas-Wheeler on his shoulder, the 19-year old centre with great feet to drift past his man to score his first Ospreys try. Davies converted to level it.
Thomas-Wheeler, Harri and Luke Morgan then combined well up the left flank to take their team 80m upfield, eventually winning a penalty on the Pau line only to lose the ball at their own lineout.
They did get over the line though just a couple of minutes later. Kotze's first try came from a line out on the right and with an advantage after Pau had brought down the maul illegally Davies freed the South African. He was half tackled but it was ruled not complete and he got back to his feet to saunter over, Davies with the extras.
Pau brought up the hour with their second try, coming off a long spell of pressure, with a penalty advantage in their favour, creating space for skipper Daniel Ramsay to go under their posts. Hastoy converted and it was all-square but the Ospreys led again just two minutes later.
It was Kotze celebrating a double as he made a great run, jinking feet taking him clear before he exchanged passes with Mathew Aubrey to score his second, Davies again on target.
A see-saw contest swung back Pau’s way as it moved into the final fifteen minutes, Colin Slade’s pinpoint cross kick to the left wing where it was worked to Pierre Nueno to race over.
The conversion was good and the scoreboard was level once again at 21-21.
As the clock ticked down, the next score was crucial and it went the way of the home team, a powerful drive from a lineout on the left rounded off by Laurent Bouchet. The conversion was missed which meant Pau held a five minute lead with the same number of minutes remaining.
Try as they might, the Ospreys were unable to find their way through Pau’s defence one more time, eventually conceding possession inside the opposition half with the clock red as they tried to make something happen.
The focus now returns to the Guinness PRO14 with a vital game against Glasgow at Scotstoun on Friday night.