American Denis Kudla was made to work for his second-round berth after rallying to beat Mischa Zverev at the US Men's Clay Court Championship.
Kudla dropped the opening set but bounced back to win consecutive tie-breaks for a 3-6 7-6 (7-2) 7-6 (7-2) victory in two hours, 31 minutes in Houston on Monday.
After tying the match at a set apiece, Kudla found himself trailing 4-2 in the decider but fought back to level proceedings.
And Kudla, who had a match point on Zverev's serve at 6-5, then reeled off five consecutive points in the tie-break before eventually clinching a rare win on clay.
In fact, it was Kudla's first clay win at ATP Tour level, having lost his three previous matches in Monte Carlo, Houston and Roland Garros.
Next up for Kudla is top seed John Isner.
Past champion Juan Monaco survived a late rally to defeat Gerald Melzer in three sets.
Monaco - winner of the tournament in 2012 - held his nerve in a 6-2 6-7 (3-7) 6-4 win.
Meanwhile in Monday's only other match, Hyeon Chung upstaged Victor Estrella Burgos 6-4 6-7 (7-5) 6-0.