Barthel was on the court a mere 35 minutes in a shutout of Chiara Scholl. She won three-quarters of the points on serve, not facing a break point, and nearly 70 percent off Scholl's serve.
No. 3-seeded Irina-Camelia Begu also had a solid win, ousting German wild-card entrant Carina Witthoeft 6-3, 6-3. Begu saw her serve broken four times but she had seven breaks of her own in nine games receiving.
Also Monday, eighth-seeded Karin Knapp defeated Valeria Solovyeva 6-3, 6-2 but Arantxa Rus posted the first upset of the tournament with a 7-5, 5-7, 7-4 decision over No. 7-seed Maria-Teresa Torro-Flor.
Rus totaled seven breaks -- against six for Torro-Flor -- in snapping a WTA record-tying 17-match losing streak. The only other player to lose 17 consecutive WTA matches was Sandy Collins in 1984-87.
Rus had last won a WTA main draw match last August in the first round of a tournament in Dallas. The losing streak caused her ranking to drop to No. 262.
Swim Week Miami Beach 2014 [PHOTOS]