They toppled high-flying Nottingham Forest 1-0 at Basford United FC to reach the final of the FA Women's Premier League Cup.
Avilla Bergin finished from Eartha Pond's cross to secure the win in the second half.
It's considered the biggest competition Spurs can realistically win with Women's Super League clubs dominating the FA Cup and therefore Sunday's semi-final success at Forest has to be one of the biggest wins in the club's history.
Spurs will now play either Blackburn or Cardiff in the final scheduled for Kidderminster on May 8. The Ryman Cup Final (April 14) and Capital Cup Final (April 27) are also in the bag.
The League Cup is the 'national' cup for Spurs with both Northern and Southern Divisions of the FAWPL competing.
Forest are challenging for the Northern Division title with nine wins and just two defeats in 13.
"This is a huge achievement and something the players can all be proud of," said manager Karen Hills.
"We said from the start of the season that this was the competition we really wanted and to get to the final says everything about how far we've come. I can't praise the squad highly enough, the players have been excellent.
"We knew Forest were a good side but we controlled the game for long spells. The back five defended well, Toni-Anne Wayne made saves when she needed to and we created chances throughout.
"We believed we could do it and to go out and get the decisive goal and then see the game out how we did speaks volumes."
NOTTINGHAM FOREST 0-1 SPURS
FA Women's Premier League Cup, semi-final
Report from Khalid Karimullah at Basford, Nottingham
After reaching the Ryman and Capital Cup finals respectively, Tottenham Hotspur Ladies travelled to Nottingham Forest for their FA Women's Premier League Cup semi-final, aiming to reach a third showpiece.
Spurs started well. Bianca Baptiste drifted into space on the edge of the area and unleashed a ferocious drive which forced a great save from Vanessa Kinnerley before dipping a second effort just wide.
With more Spurs pressure continuing to arrive, Jenna Schillaci's precise corner almost arrived at the head of Wendy Martin, as Kelley Kennaugh was forced to get a vital touch on the ball. From the following corner, Baptiste's in-swinging delivery found Martin, who placed her header from close range over the bar.
Minutes later, Avilla Bergin did well to create space for herself before breaking away for a one-on-one chance, though her attempted lob over Kinnerley was denied at the last second. With the hosts starting to show signs of their attacking prowess, Schillaci made a vital clearance to deny a cutting pass from Jemma White, otherwise Andrea Bell would have been through on goal.
Martin then forced a back-pass from White, which gave Bergin another great chance. Kinnerley again made a vital stop with the ball subsequently falling kindly to Martin, she could only place her side footed attempt into the hands of the keeper.
Just before half-time, a great chance fell to Natasha Meade, who couldn't get a vital touch on Bell's fine delivery. Meade then had another chance from inside the area, forcing Alex Keown to ensure her half-volley couldn't trouble Toni-Anne Wayne.
It was a similar pattern in the second-half, as Baptiste's shot was deflected into the path of Ronnell Humes, who forced Kinnerley to palm her effort onto the crossbar. Following a spell of Forest pressure, Wayne did brilliantly to get a finger tip on Kennaugh's close range header, as she tipped the ball onto the post.
With the game starting to open up, a deserved goal, and winner, arrived 19 minutes from time. Eartha Pond's teasing cross from the left was glanced to the far post by Leah Rawle, as Bergin rushed in and squeezed her effort into the net via the post.
Spurs Ladies: Toni-Anne Wayne, Lucia Leon, Leah Rawle, Sophie McLean, Alex Keown, Avilla Bergin, Bianca Baptiste, Wendy Martin (Eartha Pond 56), Jenna Schillaci (capt), Riana Soobadoo (Kelley Blanchflower 86), Ronnell Humes (Rosie Kmita 82). Substitute (not used): Barbara Holmark.
Player of the Match: Avilla Bergin