The Hero Indian Super League (ISL) has seen nerve-wracking knockout matches over the seasons where the two teams locking horns have often fought tooth and nail in the bid to reach the final.

This has resulted in the supporters witnessing some of the finest moments in the league's history with defending champions being toppled, underdogs proving their mettle and the tension and the drama reaching the ultimate peak.

As we get ready to witness knockout football in the Hero ISL once again, here is a list of some of the most thrilling knockout matches in the league's history:

Chennaiyin FC 3-1 Kerala Blasters FC, Semi-final second leg 2014 season

The first-ever season of Hero ISL witnessed the clash of the two southern rivals Chennaiyin FC and Kerala Blasters FC in the semi-final. The Yellow Army made a perfect start to the story with a 3-0 victory in the first leg at home.

The second leg saw the Marina Machans welcome the Yellow Army in front of a packed home stadium with a three-goal deficit to overturn. Following a goalless first half that saw Jamie McAllister sent off for Kerala Blasters FC, the home team turned the tie on its head in the second half, with goals from Mikael Silvestre, an own goal from Kerala Blasters FC's Sandesh Jhingan and a 90th-minute goal by Jeje Lalpekhlua to make it 3-3 on the aggregate as the roof went off at the Marina Arena.

With the match into extra time, Chennaiyin FC were handed a major blow after marquee player Marco Materazzi saw red. With both sides down to ten men, the Blasters managed to score the decisive goal through Stephen Paul to nudge them ahead on aggregate before forward Bojan Djordjic received his marching orders as Chennaiyin FC finished with nine men. The visitors reached their first-ever final and Chennaiyin FC's hearts were broken in the most dramatic way.

Delhi Dynamos 2-1 Kerala Blasters, Semi-final second leg 2016 season

Kerala Blasters FC made it to their second semi-final in three years in 2016. They made the perfect start as they won the first leg at home with a solitary goal from Kervens Belfort in the 65th minute. The clash was filled with crunching tackles, high temper and players rounding up the opponents. 

The tie resumed with the second leg started where it had left off in the first one. Delhi Dynamos FC applied pressure from the first whistle and their efforts paid off after Marcelo Pereira put the home team in front in the 21st minute. Kerala Blasters FC were quick to respond and Duckens Nazon equalised for the visitors in the 24th minute. Two goals in four minutes changed the whole tempo of the match and just three minutes later Delhi Dynamos' Milan Singh was sent off for a tackle on Mehtab Hossain.

Gianluca Zambrotta's men were at a disadvantage with the sending off but a free-kick at the stroke of half-time saw Ruben Rocha Moya head past Sandip Nandy to give the home team the lead heading into half-time. The match went into penalties after no goals were scored in the second half and extra time despite both teams trying their best. The Yellow Army rode on three consecutive penalty misses from Delhi Dynamos FC and booked their ticket to the final with a 3-0 penalty shootout win.

Bengaluru FC 3-1 FC Pune City, Semi-final second leg 2017-18 season

Bengaluru FC played their first-ever Hero ISL season in 2017-18 and the Blues displayed their quality by making it to the semi-finals in their first year. FC Pune City hosted Albert Roca's side in the first leg and neither team were able to convert their chances in a goalless affair.

The Blues welcomed FC Pune City at the Sree Kanteerava Stadium for the second leg and it was Sunil Chettri's night. With Bengaluru FC leading 2-0 through Chhetri's double, Jonatan Lucca of FC Pune City scored in the 82nd minute of the game to unsettle Albert Roca's side but the Blues skipper scored again in the 89th minute to complete his hat-trick and send the Blues to their first-ever final after a nervy evening where the visitors had put the hosts to test.

Mumbai City FC 1-5 FC Goa, Semi-final first leg 2018-19 season

FC Goa and Mumbai City FC clashed to fight it out for a place in the Hero ISL 2018-19 final. The Islanders drew the first blood as Rafael Bastos put the hosts in front in the 20th minute as the home fans went into a frenzy.

However, the Gaurs had other plans, scoring five goals in reply. Jackichand Singh scored the equaliser in the 31st minute which was followed by Mourtada Fall's brace, a goal each from Ferran Corominas and Brandon Fernandes that saw Gaurs take a massive advantage into the second leg. The Islanders failed to hold their fort as an impeccable display of creativity, fluidity and attacking mindset by FC Goa led to one of the biggest scorelines in Hero ISL knockout stage history.

FC Goa 4-2 Chennaiyin FC, Semi-final second leg 2019-20 season

Reaching back-to-back semi-finals, FC Goa were at the peak of their powers in the 2019-20 season but they met their match in the semi-finals in form of a resilient and fearless Chennaiyin FC. The Marina Machans overwhelmed FC Goa in the first leg which ended 4-1 in the home side's favour.

The second leg was expected to be another entertaining affair and both teams delivered on the big stage once again. It was FC Goa's turn to put the Marina Machans under pressure. The match began with an own goal from Lucian Goian that put the Gaurs in front. Mourtada Fall then scored in the 21st minute to give a two-goal lead to the home team. A high-scoring second half saw Lallianzuala Chhangte score for the visitors before Nerjus Valskis slotted past Mohammad Nawaz to bring Chennaiyin FC level on the night and restore their three-goal cusion on aggregate.

The Gaurs then breathed life back into the tie with two quick-fire goals from Edu Bedia and Fall in the 81st and 83rd minutes respectively. FC Goa kept threatening Owen Coyle's side but in the end Chennaiyin FC prevailed by just a one-goal margin in a tie that saw eleven goals being scored. 

Mumbai City FC 0-0 FC Goa, Semi-final second leg 2020-21 season

A repeat of the semi-final from the 2018-19 season, FC Goa and Mumbai City FC were again standing in each other's way for a place in the Hero ISL final. The tie had extra spice added to it with former FC Goa head coach Sergio Lobera leading the Islanders against the Gaurs.

The first leg ended in a 2-2 draw. Both teams came close to gaining the advantage going into the second leg but had to be content with a draw. The second leg witnessed attacks at both ends with players coming close to scoring the all-important goal for their respective teams. In the end, the match had to be decided via the penalty shootout as the score stayed 0-0 at the end of the extra time.

Phurba Lachenpa who came in as a substitute in the 120th minute to replace Amrinder Singh vindicated Lobera's brave decision by making two brilliant saves in the shootout. Mumbai City FC won 6-5 on penalties and made it to their first-ever Hero ISL final.