England ended Thursday on 303-9 in its second innings after 77.4 overs — a lead of 181 with one wicket left — after lightning and rain ended play with Ireland still threatening to pull off one of test cricket's biggest-ever upsets.
With the game so finely poised all three results remained on the table after Leach came to England's rescue. The left-hander vaulted from No. 11 to an emergency role at the head of the innings late on day one and went on to share a stand of 145 with debutant Jason Roy, who scored an attacking 72.
By the time the pair had steered the score to 171-1, Ireland seemed in trouble on a sweltering afternoon, but the visitors rallied by claiming the next seven wickets for 77 as England collapsed to 248-8. Sam Curran smashed a rapid 37 to give England valuable late runs.
Newcomer Mark Adair took 3-66.
On Wednesday, 10 days after celebrating a dramatic World Cup final win against New Zealand in the ODI format at Lord's, England was humbled at the home of cricket against lowly ranked Ireland.
England was dismissed for 85 in 23.4 overs on the first morning of the four-day test — the first such encounter between the inventors of the game and one of the latest teams to join the sport's elite.
Ireland replied with 207 in its first innings, with Andy Balbirnie scoring 55 and Paul Stirling making 36, to take a 122-run lead before being bowled out just before stumps.
Ireland is only playing for the third time at test level. England, meanwhile, has played 1,010 test matches since 1877.