Poulter had five birdies on the front nine - four on lengthy putts - and the Englishman had a 54-hole total of 13-under 203 on the Kingston Heath sand-belt course.
Poulter's 9-iron approach on No. 18 nearly holed out from the fairway and he had a tap-in birdie to finish.
"I just hit it, let it ride up the crest and feed down," Poulter said. "It turned out to be a decent shot. ... When you go out with a reasonable breeze and you produce a score like that, you have to be happy."
Scott, who shot 67, stayed close until consecutive bogeys on 16 and 17. However, a 15-foot birdie putt on 18 pulled him back within one shot of Poulter and a final-round pairing with Poulter on Sunday.
"In the end, I really needed it," Scott said of his birdie on the last. "With being just one shot behind, it can all change pretty quickly out there. He (Poulter) got off to such a great start, I was happy to be able to stay close."
Australian Matthew Guyatt, leader by two strokes after each of the first two rounds, shot 75 Saturday and was six strokes behind in third.
Guyatt birdied the par-5 first and didn't get another until the 15th, but followed that up with a double-bogey on 16 and a bogey on the last.
Graeme McDowell, the 2010 U.S. Open champion from Northern Ireland, shot 67 Saturday to move up the leaderboard after just scraping in on the 4-over cut line on Friday after a 77.
"They've put their trust in me to come down here this week," said McDowell, who was 12 strokes behind Poulter. "I was panicking a little bit down the stretch yesterday. I felt so out of sorts within myself. I knew I had to try to make the weekend.
"I was early to bed last night because pride kicks in. I wanted to go out there this morning and do my job."