The world No. 14 beat Annika Beck, 2-6, 6-1, 6-3.
The top four seeds won their opening-round matches.
The wild card and former No. 8 had been out for 17 months after two foot surgeries.
The men's and women's champions will receive $2.85 million.
The Brit believes Djokovic's Slam title will "climb to 11, 12, 13 and maybe more."
Thoughts on Nadal, Sharapova, and their pre-Paris struggles.
Djokovic leads the race to Paris, but is Nadal right where he wants to be as well?
Unlikely hero Simona Halep has endeared herself to fans with a refreshing style of play.
Nerves and Novak: Can Rafael Nadal fend off both of these obstacles?