Gauff, ranked 20 places above her opponent in the WTA rankings, was playing in her first tournament since advancing to the third round of the US Open, where she fell to then-world No. 1 Naomi Osaka.
But after beating Russia’s Ludmilla Samsonova on Sunday in the first round of qualifying, the 15-year-old was ousted in 74 minutes by Kotpatsch.
Gauff was dominant in the early stages, breaking the German in the very first game of the match before winning her first 10 points on serve.
But her dominance wouldn’t last, wasting an opportunity to claim a second break in the third game before being broken herself in the fourth.
Kotpatsch would go on to seal the set, breaking Gauff once more in the final game of the set.
The second set started with Gauff again on top, breaking Kotpatsch’s serve early, but a combination of unforced errors and double faults saw the American squander her advantage — allowing her more experienced opponent to ease through the rest of the second set and claim her place in the tournament’s main draw.
Gauff is now set to compete in the doubles draw with fellow American Caty McNally before entering the qualifying draw at next week’s Luxembourg Open.