The American largely struggled on serve over the course of 63 minutes, as she hit five double faults and won just over 40 percent of the points played in the games in which she was at the line.
After breaking Halep for the first time in the match in the third game of the second set, Townsend proved unable to stay level with the reigning Roland Garros champion for much longer.
The decisive break for the Romanian came in the sixth game, as the 22-year-old left-hander double faulted twice to hand the two-game cushion back to the No.2 seed, and Halep lost just one point in her last two service games to get over the finish line.
While she was scheduled for a possible third meeting against Lesia Tsurenko in the last four weeks in the round of 32 when the draw was released, Halep will instead face lucky loser Polona Hercog up next.
Tsurenko, the No.26 seed, was replaced by the Slovenian after the Ukranian withdrew due to an arm injury earlier on Friday.
Hercog made good on her second chance, defeating Japanese qualifier Misaki Doi in straight sets, 7-6(4), 6-4.
“Against Hercog, I know she has a big forehand, serve is good,” Halep assessed. “I just have to adjust myself on the position on court and we will see.”