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Tonbridge face a midweek away game in the Bostik Premier play-offs after losing on Saturday.
Angels were second-best at lowly Potters Bar, on a day when they needed to win to give themselves home advantage on Thursday night.
Instead, Steve McKimm's side - who close the season in fourth spot - face a trip to third-placed Haringey.
A gusty wind and bobbly pitch didn't make for an entertaining encounter, although the visitors did seem to be on top early on.
Joshau Hutchinson headed Andrew Lomas' cross at Tonbridge keeper Jon Henly before Angels were dealt an injury blow ahead of this week's play-offs.
Tom Beere went down after a midfield challenge and, following seven minutes of treatement, he left the field on a stretcher.
The hosts took the break in their stride and went ahead just past the half-hour, Marvin Morgan bursting through a hole in the Angels defence and rounding keeper Jon Henly to open the scoring.
Angels threatened with long-range efforts from Jared Small and Craig Stone but home keeper Berkley Laurencin was hardly called into first-half action.
Tonbridge were left facing an uphill struggle seven minutes into the second half when Potters Bar added a second. Nana Keyi exchanged passes with Morgan in the box and then finish beyond Henly from an angle.
Hutchinson should have made it 3-0 when he blazed over from close range but Angels got themselves back into the game midway through the second half when Sonny Miles bundled home a corner at the far post.
Angels thought they had levelled matters four minutes from time but Chinedu McKenzie's close-range effort was ruled out for offside.
It was not to be on the day for Angels but their season is far from over and they now go into the play-offs on Thursday night at Haringey.
Potters Bar: Laurencin, Powell, Lomas, Nicholas, Budden, Grace, Wynter, Sach, Hutchinson (Cochrane 76mins), Morgan, Kyei. Subs not used: Vassell, Cole.
Tonbridge: Henly, Smith, Parter, Beere (Theobalds 32mins), Miles, Lee, Small, Stone (Ramadan 46mins), Read (Derry 60mins), McKenzie, Turner. Subs not used: Folkes, Adonis-Taylor.
Attendance: 315.