* Williams strong after losing first set
* Testy exchange breaks out in second
* Trophy is American's 49th as pro (adds details, quotes)
April 7 (Reuters) - World number one Serena Williams bounced back from a set down to defeat former top ranked Jelena Jankovic of Serbia 3-6 6-0 6-2 and win her third Family Circle Cup title on Sunday.
The triumph was American Williams' 49th in WTA play. Only nine players have won 50 or more WTA titles.
After dropping the first set in 45 minutes, Williams cruised through the next two, winning 12 of the final 14 games for her second consecutive title on the clay at Charleston, South Carolina. She also won in 2008.
Williams stepped up her play after a testy exchange in the first game of the second set.
The American held up her racquet as Jankovic served, signaling she felt Jankovic served before she was ready.
"How long do I have to wait?" the Serb asked the chair umpire.
"Until I'm ready," Williams replied.
Williams won the next eight points.
"I just got really relaxed and was like, 'Serena, you have to chill out and not get crazy and if you win, great. If not, you're trying,'" Williams told reporters.
More consistent play aided the turnaround, she said.
"I felt so close in that first set," said Williams, who has now won 71 of 75 matches since the start of last year's clay court season.
"I felt like I could have been up 3-0. She was playing really, really well, but it was just a shot here, a shot there, and she played really well in the big points.
"I had so many opportunities that I missed. She took advantage of all of that, and she went on to glory in that first set."
Jankovic said she began to tire as the match continued.
"In the second set I had 40-15 in that first game and then again in another couple of games I had 40-15, 40-0. I should have focused and gotten those games," said the Serb.
By the third set, Williams' strong play began to affect her, Jankovic said.
"I got tired," the world number 18 said. "It was my sixth match here and playing Serena is not easy - you have to run a lot of balls down and hit as hard as you can and give your maximum.
"She's so strong. She's the No.1 player in the world for a reason.
"She was the better one at the end." (Reporting by Gene Cherry in Salvo, North Carolina, editing by Mark Meadows)