The striker made an instant impact off the bench in the second half to help the Seasiders on their way to the three points.
Albie Morgan and Andy Lyons were also on the scoresheet for Neil Critchley’s side in the win at Bloomfield Road.
Jake Beesley had two chances inside the opening seven minutes.
For the first, he couldn’t quite sort his feet out after an error from visitors inside their own box, with Fabian Mrozek quickly coming off his line to deal with the situation.
The Liverpool keeper came out on top once again shortly after, denying a curling effort from the Seasiders striker with a fantastic save.
Opportunities also came the way of Albie Morgan and Karamoko Dembele, with both players unable to find the target.
The Premier League U21s side took the lead just before the half hour mark.
A great ball was played through to Paul Glatzel, who slotted past Richard O’Donnell.
Ahead of half time, Critchley’s side pulled level.
A ball over the top saw Beesley brought down by Mrozek on the edge of the box, with the Seasiders forward about to go around the keeper who had come off his line to deal with the situation.
The visitors had a defender in support, seeing the man between the sticks avoid a red card.
From the resulting free kick, Morgan curled a superb effort off the post and in to level the scores.
During the break, Dembele was replaced by Kouassi- who made an instant impact.
Within 30 seconds of the restart, the summer signing was on the scoresheet, with a great finish past the Liverpool keeper.
Moments later, the Seasiders had the ball in the back of the net again, but the linesman’s flag was raised for offside.
Liverpool pulled themselves back level just after the hour mark.
O’Donnell did well to save an initial effort, but Musialowski was on hand to finish the rebound.
Blackpool reclaimed the lead with just over 15 minutes remaining, with Kouassi guiding in a great cross from substitute Kwaku Donkor.
Heading into the latter stages, the Seasiders secured the three points.
Once again, Kouassi found himself in space, and slotted past the Liverpool keeper to complete his hat-trick.
Before the full time whistle, Lyons also added his name to the scoresheet, as he claimed his first goal of the season.
Here’s how the Seasiders performed:
1. How did the Seasiders perform?
We've taken a closer look at how Blackpool performed against Liverpool U21s. Photo: CameraSport -
2. Richard O'Donnell- 7
Blackpool's cup keeper returned to the starting line-up for the game against Liverpool U21s. Despite making some good saves, there wasn't much he could do about the two goals for the visitors. Photo: CameraSport - Andrew Kearns
3. Doug Tharme- 7
Doug Tharme came into the side for his second start for Blackpool. The defender looked strong at time, but when Liverpool got forward they were able to cause problems for the Seasiders back three. Photo: CameraSport -
4. Marvin Ekpiteta- 6
Marvin Ekpiteta looked a little nervy at times in the game against Liverpool. He made his return to the starting line-up after missing out in the last few league games. Photo: CameraSport - Dave Howarth
5. Will Squires- 7
Will Squires was handed his debut by Neil Critchley. While he was up against Liverpool's youngsters, the experience of being alongside some of Blackpool's senior players will prove to be beneficial. Photo: CameraSport -
6. Owen Dale- 7
Owen Dale enjoyed some bright moments but his final pass could've been better at times. He received a warm applause following his substitution in the 63rd minute. Photo: CameraSport - Lee Parker