The second seed faced Frenchman Corentin Moutet, who was runner-up in Doha earlier this season. Moutet displayed some impressive form, fighting from a set down to upset Pella 6-7(4) 7-5 6-3.
After claiming the first set in a close tiebreaker, Pella actually served for the match at 5-4 in the second. However, he succumbed to his nerves and Moutet was able to reel off three consecutive games to level the match.
Moutet was able to maintain his rhythm and break the Argentine in the final set, before serving out the match to win the three hour slugfest.
He next faces Slovakian Andrej Martin, who saved all four break points to beat Spanish qualifier Carlos Taberner 6-3, 7-6(7). Taberner was coming off an upset victory over Fernando Verdasco but failed to maintain his momentum.
Sixth seed Pablo Cuevas defeated Italian Gianluca Mager 6-7(5) 7-6(2) 6-1 in two hours and 20 minutes. The Uruguayan has won all six of his ATP Tour-level titles on clay, with his most recent being at Sao Paulo in 2017.
Cuevas will now face third seed Cristian Garin, who dispatched of unseeded Hungarian Attila Balazs 6-3 6-0 in just over an hour.
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