Ben Shelton will go no further in Hamburg. The second seed at the ATP 500 event was eliminated in the round of 16 by Daniel Altmaier, 4-6, 7-6(4), 6-4, on the clay courts of Am Rothenbaum on Tuesday.

Shelton had started the tournament with a hard-fought first-round victory. But against Altmaier, carried by his home crowd, the script flipped. After taking the opening set, Shelton saw his German opponent raise his level. The second-set tiebreak swung Altmaier's way, and the momentum never returned to the American's side.

In the decider, Altmaier held onto his break advantage and shut the door on any comeback attempt. A prestigious win for the 27-year-old German, who has shown his ability to trouble top seeds at major events before, particularly at Roland-Garros.

For Shelton, this early exit raises questions just a week before the main draw begins in Paris. The 23-year-old American, who reached the quarterfinals at Roland-Garros last season, will need to quickly find his clay-court form.

Elsewhere in Hamburg, Ugo Humbert battled through in three sets against Justin Engel (6-3, 3-6, 7-6), while , the top seed, dispatched Vit Kopriva 7-5, 6-1.