Barthel has been ranked as high as No.23 in the world and has two WTA titles to her credit but came into Nürnberg having lost in qualifying or the first round of the main draw in 10 straight events.
Against promising Swiss teen Belinda Bencic, Barthel won six of seven points from 3-1 down in the first set tie-break and collected the lone two breaks of the match in the first and last games of the second set for the 7-6(4), 6-3 triumph.
Barthel ended up two for two on break point opportunities and saved all six break point chances on her own serve. She also won 38 of 42 points on her first serve.
"It was a really tough match," Barthel said. "She has been playing really well recently, and she's so young. We had never played against each other and I didn't really know what to expect. I was just trying to play my game. We had a really close first set but I'm happy that I got through it and won it in two sets.
"Next I may play against another German, Beck. We've played two times already this year. We'll see. She has a tough draw against Cepelova. I've never played her, but I'm just happy to be in the second round and to have another match here."
Polona Hercog was a 1-6, 6-2, 6-1 winner over third-seeded Klara Koukalova, which was an upset on paper, but was hardly a surprise considering she is now 7-0 against the Czech. Down a set and a break, Hercog only surrendered two more games the rest of the way. Interestingly enough, Hercog also beat Koukalova in the first round here last year.
"I started a little bit slow and Klara started fast and was playing great," Hercog said. "It was not easy to get into the match, but I'm really happy the way I turned it around."
Hercog is playing just her fourth event of 2014 after a right rib injury kept her out of action much of the early part of the season.
"The conditions are not easy, but I'm really happy to get this win after all my injuries and am looking forward to the next match," Hercog said.
The qualifiers were also determined Sunday, with Julia Glushko, Anastasia Rodionova, Nina Zander and Beatriz García Vidagany all securing main draw spots. Montserrat González also made the draw as a lucky loser replacing Roberta Vinci.