When lightning flashes and rain cut short the second day's play in a match scheduled for four days rather than the usual five for a Test, England were 303-9 in their second innings - 181 runs ahead.
That represented a colossal improvement on their humiliating first-innings 85 all out but once again their batsmen struggled ahead of next week's first Ashes Test at Edgbaston.
England had been well-placed at 171-1 second time around, a score built on a partnership of 145 between nightwatchman Jack Leach, who made 92, and Test debutant Jason Roy (72).
But England's top-order let them down again, with seven wickets falling for 77 runs either side of tea as they slumped to 248-8 on a ground where just 11 days earlier they had won the World Cup.
Sam Curran, not for the first time in his short England career, added valuable lower order runs with a brisk 37 before he holed out and Stuart Broad was 21 not out at stumps.
Ireland are playing in just their third Test, with the visitors losing on debut to Pakistan last year and against fellow newcomers Afghanistan in March.
But that did not stop them routing England on Wednesday, with seamer Tim Murtagh taking a superb 5-13 on his Middlesex home ground.
Fellow paceman Mark Adair, who led Ireland's attack on another hot day with 3-66 on Thursday, told the BBC: "Conversations this morning were about us bowling England out.
"These lads are good cricketers, they've played a lot of cricket, so it was nice to get them."
England resumed on Thursday on their overnight 0-0 after Ireland had made 207, featuring Andrew Balbirnie's 55.
Unexpected opener Leach, who survived a Murtagh maiden on Wednesday, played watchfully but made the most of any loose deliveries.
"It was very surreal, in front of the Lord's crowd," said Leach.
"I've scored one hundred for the Somerset 2nd XI and that's literally the only hundred I've ever scored. It wasn't to be but I still would have taken 92 at the start of the day."
Meanwhile Leach reckoned England might already have enough runs on the board to set up a win.
"We've got to move on quickly because the Ashes are round the corner. For now, it's just thinking about tomorrow (Friday) and we're confident we've got enough in this game."
Left-hander Rory Burns fell for six when he pushed hard at a Boyd Rankin delivery and edged a simple catch to wicketkeeper Gary Wilson.
But Leach went to 47 with a straight-driven four off Stuart Thompson before his edged boundary through third man off the medium-pacer saw the Somerset left-arm spinner, playing his first Test at home, to his fifty.
Roy, looking to fill England's problem position of opener after his World Cup heroics, cut Thompson for his seventh four to complete a 47-ball fifty in just his second Test innings.
But the attacking batsman was denied a century on debut by a Thompson in-ducker that bowled him.
The bespectacled Leach, having surpassed his previous first-class best of 66, was dropped twice until eventually a defensive edge off Murtagh was held at second slip by Adair.
Leach, who had been in sight of an achievement that eluded batting greats Brian Lara, Ricky Ponting and Sachin Tendulkar - a Test hundred at Lord's - walked off to a standing ovation after batting for 220 minutes and facing 162 balls, hitting 16 fours.
Joe Denly was then needlessly run out after being sent back by captain Joe Root when the skipper was already two-thirds of the way down the pitch.
England's slump continued when World Cup-winner Jonny Bairstow was lbw to Adair for his second duck of the match.
Root, who took 64 balls to make 31, tried to break free by going down the pitch to Adair only to see an edged drive well caught high to his right by the diving Wilson.