The 25-year-old Romanian, runner-up at this year's French Open, needed just 79 minutes to advance past 957th-ranked Stephens on the Washington hardcourts as she starts preparing for the US Open that begins August 28.
"It was a tough first set. I was missing a little bit too much and she made some shots," Halep said.
"For first match on hardcourts, it wasn't that bad. I missed a few shots. Didn't have the rhythm at the beginning, but I feel better now."
Stephens has only been playing for a month after missing nearly a year with a left foot injury. She remains frustrated as she tries to regain the form that saw her claim her first WTA title in Washington in 2015.
"It was a good first set," Stephens said. "I did well to do the best I could. I got a little frustrated in the second set. It's going to take a while to get that consistency back and get more matches under my belt."
Top seed Halep will face Colombia's 115th-ranked Mariana Duque-Marino for a quarter-final berth.
"My serve wasn't the best but I was OK. Everything went well. I can't say I have to adjust something," Halep said.
"It was important I won today. It was important the second set was much better. The next round I have to be a little more aggressive. I have to come to the baseline and finish the points sooner."
Reigning Olympic champion Monica Puig of Puerto Rico and Russian seventh seed Ekaterina Makarova each ousted US qualifiers to book a second-round meeting.
Puig defeated Louisa Chirico 6-4, 6-4 and Makarova beat Jamie Loeb 7-6 (7/4), 6-3.
Romania's Patricia Maria Tig edged Britain's Heather Watson 7-6 (7/4), 7-6 (7/3).
On the men's side, Austrian top seed Dominic Thiem was set to face 96th-ranked Swiss Henri Laaksonen in a later second-round match while Japanese second seed Kei Nishikori was to meet American Donald Young.
source: news.abs-cbn.com
