This match was not won by a moment of great quality, but it was not a game of great quality either, and Tottenham hardly cared as they celebrated coming back from a goal down to qualify for the first women’s FA Cup final of their history. Against Manchester City in the quarter-finals they conceded early, equalised late and won on penalties and it looked like they were ­following a similar template on Sunday until Martha Thomas won it with two ­minutes of extra time remaining.

After an entertaining start the quality dropped as the pressure rose, and in 30 additional minutes the closest either side had come was when Jutta Rantala’s free-kick was tipped on to the underside of the bar in the 99th minute.

But with penalties appearing increasingly inevitable Olga Ahtinen’s corner was half cleared, Matilda Vinberg sent it back in, it was flicked on at the near post and the Leicester defender Aileen Whelan headed into Thomas, and the ball looped beyond Lize Kop and into the net.

Related: Tottenham Hotspur 2-1 Leicester City (aet): Women’s FA Cup semi-final – live

Finally the great ­majority of the 18,078 fans were back on their feet. Most had been issued with Spurs flags on their way in, and a while earlier had created an inspiring spectacle as they waved them in the late morning sunshine as the players entered the field. Leicester laid on six coaches to bring their fans to London, one of whom had brought an impressively large and resonant drum, but if at first they filled a single forlornly flag-free block soon it was they who were cheering most loudly.

Spurs started well and might have scored twice in the first 10 minutes only for Celin Bizet, both times set up by Grace Clinton, to shoot – first too close to the goalkeeper and second not close enough to the goal. But in the 12th minute Leicester took the lead: CJ Bott carried the ball through midfield before passing to Rantala, who was allowed to cut inside too easily and from 20 yards blasted a left-foot shot beyond the reach of Becky Spencer.

Leicester dominated the period immediately after the goal and could have scored another when Deanne Rose pulled the ball back to Sam ­Tierney, but the finish lacked ­conviction and Spencer saved with her feet. Near the end of the first half Rose ran on to an underhit backpass but lost her footing as she attempted to shoot, and within 20 seconds of the restart when ­Rantala played in Lena Petermann, who delayed her shot long enough for Luana Bühler to get in the way of it.

“Everybody looks at us as ­little Leicester but we’re not little ­Leicester, and we’re putting ourselves on the map,” said Jennifer Foster, their interim head coach. “We all need to look at this as learning. We’ve got a lot of experience in our team but a lot of them won’t have played in an FA Cup semi-final before. There’s ­lessons to be learned, we’ll just have to improve on it next time. We’re building momentum and we know where we want to be, and it’s a really exciting journey to be on.”

Even if they avoided a disastrous start, the second half was largely dismal for Tottenham, and it took until stoppage time for them to put together a spell of pressure. By then they were level: Jessica Naz had only just moved from the right to centre-forward when the former Spurs ­captain Josie Green completely missed her kick, allowing the 23-year-old to sprint clear before finishing coolly. From there Spurs should probably have won without ­requiring extra time, both Thomas and ­Charlotte Grant coming close.

“We haven’t won anything yet,” said Robert Vilahamn, the Spurs coach. “We’re not going to be ­favourites in the final, but that’s fine. We need to keep playing big games if we want to be a big team and win titles. We’ve shown this year we can develop players and play good ­football, but some players who want to come to Tottenham also want to win titles, and we want to show we can do that.”