Howell was paired with US Open Champion Rory McIlroy – the man who finished 26 shots ahead of him at Congressional – but this time it was World Number 282 Howell that fired a superb 64 in wind and rain to charge all the way from joint 25th into a tie for the lead with Dyson and Green.World Number Four McIlroy, whose record-breaking total at Congressional gave him his first Major title by a massive eight strokes, dropped back to joint 32nd with a one over par 72, the same as compatriot Graeme McDowell
Scot Stephen Gallacher matched that score to move into fourth place, two shots behind, but halfway leader Marcel Siem double-bogeyed the 18th for a 73 and was joint fifth with defending champion Ross Fisher and Dane Søren Hansen three behind.
Howell, twice a Ryder Cup player, said: "I've not been in the best of form for quite some time, so I was intrigued how I was going to be playing with Rory.
"He's the star of world golf, but there were no nerves and the crowds were amazing.
"I think I got inspiration from the big-time atmosphere. I did everything really well and it was great.
"I've given myself a chance - that's the main thing - and I was delighted to hole a seven footer (for par) on the last. Missing it would have been a sad way to end a flawless day."
The 36 year old has only once scored better in his European Tour career, but also had a 64 on the opening day at Killarney last year.
"They're my best two rounds in a year and three days," he said. "While Rory was doing miraculous things at the US Open, I was absolutely shocking.
"We couldn't have had more polar opposite weeks, but it led me onto a lot of thinking.
"It's been a bit of a muddle for a few months, but finally last week I clicked on something that I thought was a sensible course of action in my swing thoughts.
"Nothing particularly major, but it cleared my mind a bit."
While McIlroy had two shots on the beach by Lough Leane for an opening six - he also double-bogeyed the eighth - Howell parred the first four, then birdied the fifth and seventh and had five more in a spectacular inward 31 as the wind and rain turned worse.
McIlroy said: "I'm feeling as if I need a couple of drinks or something. It was a bad start, but I got it together at the end and one over is not too bad, considering.
"I'm happy that it's going right rather than left. At least the club's out in front of me instead of being behind and flipping it over.
"It's an easy fix. It's the ones that go left I don't like.
"At this tournament you're trying so hard to play well for not just yourself, but for everyone else. Sometimes you can just find yourself trying a little too hard and pushing a bit too much."
Dyson, who finished ninth in The Open Championship a fortnight ago after being called in as a reserve just before, now has a chance to climb back into the world's top 50 and qualify for this coming week's World Golf Championships event in Ohio.