McNulty rolled in a 25-foot putt on the final hole to gain a share of the lead.
"I played nice and steady," McNulty said. "I drove the ball well. Hit some nice, quality iron shots. I'm pretty much on track with what my game's like. I balanced it all out."
Haas, winner of the Senior PGA Championship this season, parred the last six holes.
"Last year, I didn't play very well here," Haas said. "I felt like this year I needed to come out and fire away and not play too conservatively. I'm hitting the ball pretty well. Five-under, I'm pretty happy with that."