Connacht take a comfortable 22-point advantage to France in next weekend's second leg of their Parker Pen Challenge Cup tie.
The fourth-ranked Irish team were impressive against the French heavyweights and led 16-7 at the break, despite conceding the game's first points when Pau winger Rida Jaouher scored a try in the sixth minute.
Michael Bradley's men hit back through the boot of fly-half Dave Hewitt, and tries late in the first half to backrowers Michael Swift and John O'Sullivan gave them a lead they never gave up.
O'Sullivan completed his double in the second half, and home fullback Matt Mostyn wrapped things up with a late try.
The small Irish province would have won by even more if Hewitt had not missed all four conversions, but they will be wary of a wounded Pau side, whose chances weren't helped by second-half yellow cards to No 8 Bruno Bordenave and
hooker Romain Terrain.
If Connacht can beat Pau next weekend or hold them to a 21-point victory, they play the winners of the London Irish-Narbonne tie in the Cup quarter-finals.
Connacht: Tries - M Swift, J O'Sullivan 2, M Mostyn; Pens - D Hewitt 3;
Pau: Try - R Jaouher; Con - D Aucagne. Halftime: Connacht 16-7.