They were two shots ahead of England's Eddie Pepperell (65), Spain's Alejandro Canizares (68) and South Africa's George Coetzee (70), and four in front of first-round leader Oliver Fisher of England (69).
Grace's 68 featured a remarkable birdie after driving into the trees on the fifth hole. He snap-hooked a wedge to six feet to stay in contention.
"I could only hit a big, snapping hook with a wedge and when I hit it, I couldn't see the ball," Grace said of his improbable shot.
"We heard the claps and next thing you know, managed to make a nice little five-footer for birdie that definitely got it kick-started."
Wiesberger also carded 4 under, while Grillo shot a bogey-free 5-under 67 to be in contention.
Grillo putted magnificently, including a 20-foot birdie on the 11th.
"I hit the ball better today, so I've got a good feeling for tomorrow, and want to try to get my first win," Grillo said. "You have to learn first to win out here, and I've learned a lot."
Wiesberger got off to a flying start when he birdied the second and third before converting another birdie from 15 feet at the eighth.
"It's nice to start the day in the lead and hang on to keep it," he said. "It was just that bad swing on 16 which cost me a bogey there ... I finished nicely with a birdie and it gives me a bit of momentum for tomorrow."
Warren shot four birdies in his first 10 holes, but bogeyed the 14th before hitting birdies on the next two to match Grillo's score for the day.
"The last few years I've shown a lot of progress again," Warren said. "It's one thing to be confident, and to actually do it is another thing. I've definitely got a spring in the step."
Pepperell, who celebrated his 24th birthday on Thursday, carded Friday's best round of 7 under to be at 11 under with Canizares and Coetzee.
Defending champion Sergio Garcia, playing in his first 2015 event, had a forgetful day as he went out of contention at 1 under after scoring a 5-over 77. Also, Justin Rose was seven shots behind, and Henrik Stenson nine behind.