Grönefeld made her professional breakthrough in 2005, rising 54 places throughout the year. She reached the third round of the Australian Open, French Open and the US Open and played three finals in WTA Tour events throughout the season, including at the Tier II event in Beijing, although failing to win any of them. She also rose into the top 10 in the world in doubles, cementing her position as one of the most promising young doubles players on the tour at the time.