The American went out in 28 to match the lowest nine holes on the 2021 Race to Dubai and while he dropped two shots early on the back nine, a strong finish moved him to eight under at TPC Southwind.
Englishman Poulter carded a blemish free 64 to sit two shots back alongside European Tour affiliate member Carlos Ortiz and American pair Jim Herman and Matthew Wolff.
Major Champion Bryson DeChambeau was then at five under with fellow American Scottie Scheffler and Australian Marc Leishman for company, a shot clear of four home favourites in Daniel Berger, Sam Burns, Max Homa and Will Zalatoris.
English is a four-time winner on the PGA TOUR, including at this event in 2013 and twice this season, but his victory in Memphis came before the tournament had World Golf Championships status, and he is still seeking a WGC breakthrough.
Harris English: “Birdieing the first four holes is good all the time. It was just one of those rounds where you’re hitting it where you’re looking.
“Everything was working, you just kind of get in the zone. All you’re thinking are positive thoughts, you’re hitting good shots and hitting good putts so you just try and keep the gas pedal down.
“I’ll just keep doing what I’m doing. It’s my seventh time playing this course and this tournament so I feel I’ve got a good strategy.
“I’ve been working hard at home so I feel I’ll just keep doing what I’m doing, keep hitting fairways and greens and see what happens.”
Ian Poulter: “Just steady golf, to be honest with you. I’m coming off two weeks off and you never know when you’ve been at home for two weeks whether you’ve done enough practice. Practice at my home course was great fun, great to see family and friends.
“Today was one of those days where I tried to fill myself in the tournament, feel my way in and obviously I think I did that really nicely. No bogeys, clean card. Had plenty of chances, a couple of outside looks which kind of sniffed the hole, so all in all it’s a great start.
“I don’t see it as any different to any normal tournament I’m going to play in the whole season. The only thing I’m focused on is playing as well as I possibly can. I’m not high enough up in the FedExCup, I need to obviously move up in that. I’ve got two opportunities this week and the first FedEx event, so I need to move forward. Not only that, I need to pick up some points for the Ryder Cup team. So I don’t look at this as a WGC, I don’t look at that in any way, shape or form. It’s a good tournament, a course I like, so hopefully I can just continue on that.”