Dalkeith fought back from trailing 2-0 to square the cup tie at 2-2 with a last gasp equaliser only to lose out in a dramatic penalty shoot out.
Tranent had looked to have edged it at 2-1 and with only 10 men for the last quarter but Thistle’s ulimate deserved equaliser proved to be not enough.
The teams had drawn in the Premier League earlier in the season but here the Belters were 1-0 ahead in less than a minute in their first attack catching Thistle out as a cross from Tom Watters picked out Kenny Fisher who beat keeper Jim McQueen for the opener.
Dalkeith struggled to get going with McQueen by far the busier keeper in the opening 15 minutes.
On 20 minutes it was 2-0 to Tranent when from a corner Tranent’s Kenny Fisher swept the ball home.
Dalkeith faced an uphill struggle but hope arrived on 25 minutes with a brilliant overhead kick by Stewart Adams following good work up the right wing by Paul Tansey.
The second half saw Dalkeith battle for an equaliser but the Tranent defence stood firm and always looked dangerous on the break.
The visitors were reduced to 10 men in the 69th minute when Jamie Paterson was given a second yellow and subsequent red for yet another reckless foul.
This gave the home side a boost and saw a fine shot by Tansey saved by Adams.
The best Thistle chance came with five minutes left when following increased pressure a scramble in the box ended with a Ryan McQueenie header at the far post going just inches wide.
In added time Blake Wales scored the equaliser taking it to penalties.
Both opening penalties were missed with Stewart Adams shooting wide and the Belters’ keeper Adams’ own penalty hit straight at McQueen for an easy save.
Dalkeith’s McQueenie, Dean Whitson, Blake Wales all scored to make it 3-3 before John Robertson hit the post for Dalkeith to allow Tranent’s Fisher to win the game 4-3.
Dalkeith: McQueen, McQueenie, Robertson, McGlashan, Whitson, Hunter, Redpath, Greig, Adams, Tansey, Wales.