The Englishman entered the day in a share of top spot and moved ahead as he carded four birdies and an eagle to get to 18 under.
He could have been out of sight had he holed a few chances from inside 15 feet but he was still in pole position to claim a fifth European Tour title at Fairmont St Andrews.
Wallace is yet to secure a top ten on the 2020 Race to Dubai but has dropped just one shot so far this week and feels he is in total control of his game after finishing round three with two birdies, including a spectacular holed bunker shot on the 17th.
"I enjoyed it a lot," he said. "Especially the end there, to finish the way I did was really nice.
"It's probably the best I've ever handled myself."
The 30-year-old is known for showing his emotions on the golf course but was delighted at how he handled himself mentally over the Sam Torrance designed layout.
"They've been telling me if I did this it would come good at some point," he said of his work on the mental side of his game.
"So I really tried hard today. It was nice to really focus on the process rather than try and play good golf."
Overnight leaders Otaegui and Wallace both started with three pars but drove just short of the short par four fourth and got up and down to move to 13 under.
Wallace had the solo lead when Otaegui could not get up and down on the next but the four time European Tour winner soon had Porteous for company.
The 30-year-old birdied the first, got up and down from sand on the fourth, got down in two putts from off the green at the par five sixth and holed a four footer at the next to get into a share.
A putt from similar range after a stunning tee shot on the par three next edged him into the solo lead but Wallace drove the short par four seventh and holed a 20 foot left to righter to reclaim the lead.
Porteous went over the back of the tenth and the lead was extended to two but he soon hit back, hitting an excellent tee shot into the par three 11th and making the most of the par five 12th.
Otaegui had bounced back from that bogey on the fifth with a birdie on the sixth and put his tee shot to ten feet on the 11th before draining a monster putt from off the green at the 14th to briefly join the lead.
It was brief because Wallace had put his approach to four feet and duly converted to get to 16 under and lead on his own.
Wallace then holed that stunning bunker shot on the penultimate hole and got up and down from the front of the green on the last to surge ahead, with Otaegui dropping a shot on the 17th.
Crocker had a roller coaster day, eagling the seventh and making seven birdies but also dropping four shots in a 67.