Jacob Hazel scored on the stroke of 90 minutes, with the Pilgrims having trailed to Luke Woolston’s free-kick four minutes earlier.

The match headed to spot-kicks, with Cameron Gregory saving Boro’s fifth for the Pilgrims to win 5-4, but United were edged out on qualification for the quarter-finals on goals scored behind Leeds United’s under-21s.

Manager Graham Coughlan had made eight changes ahead of kick-off, with Jai Rowe, Cameron Green and Jimmy Knowles the only survivors from Saturday's trip to Tamworth.

James Gale, making his first United start, was denied by Rio Patterson-Powell's block on the line, while Gregory produced a good save to deny Ajay Matthews.

Jordan Richards crashed an effort too high, while Gregory thwarted Terrell Agyemang on the angle before the break.

Rowe saw a header hacked off the line after meeting Keaton Ward's corner, while Gale's downward header was kept out by Oliver Lloyd.

Substitute Adam Marriott saw efforts deflect narrowly wide and too high respectively, before Boro took an 86th minute lead with WOOLSTON seeing his low, angled free-kick from outside the box flying all the way home.

United responded and after Tony Weston had rattled the crossbar, HAZEL stroked home United's last-gasp leveller.

Green, Weston, Hazel, Ward and Marriott all netted for the Pilgrims, with Jack Stott, Daniel Nkrumah, Woolston and Charlie Lennon doing likewise for Boro, before Gregory's crucial save to deny Matthews.

Boston (4-4-2): Cameron Gregory; Kieran Coates, Jai Rowe, Zak Mills (Tom Leak 67), Cameron Green; Keaton Ward, Jordan Richards, Martin Woods (Oisin Gallagher 75), Sam Osborne (Tony Weston 67); Jimmy Knowles (Adam Marriott 71), James Gale (Jacob Hazel 71). Subs (not used): Frankie Maguire, Tom Donaghy (gk).

Middlesbrough (4-4-2): Oliver Lloyd; Rio Patterson-Powell (Charlie Lennon 66), George Gitau, Afonso Lindo, George McCormick; Sonny Finch (Luke Woolston 73), Terrell Agyemang, Jack Stott, Prince Acheampong (Daniel Nkrumah 73); Ajay Matthews, Finlay Cartwright (Frankie Coulson 59). Subs (not used): Hazeem Bakre, Judah Tawiah, Nathan Fisher (gk).

Referee: John Mulligan.

Attendance: 273.

PIC: Chris Bray.