Salah joined the Blues for £11m from Basel back in January 2014, after Mourinho's side beat out interest from Liverpool.
However, the winger struggled for game time at Stamford Bridge and made just 19 appearances in all competitions – scoring just twice – before leaving on loan to Fiorentina in the following season.
Salah shone in Italy with both Fiorentina and Roma, before earning his move back to England with the Reds ahead of the 2017/18 season. And the rest is history.
Liverpool's gain is Chelsea's loss and the winger is often held up as 'one that got away' for the Blues, who also failed to get the best out of a young Kevin de Bruyne around the same time.
Then manager Mourinho was asked about Chelsea's failure to keep hold of the players who would go on to become two of the top talents in world football on the The Obi One Podcast, answering: "To be honest, they left because they wanted to leave. They left because they didn't want to wait.
"History proves that their option was good because they've had the careers they have and reached a high standard, but sometimes kids make decisions like that because they can't wait, or they don't have the patience to be calm and to wait for the right moment. Sometimes their career goes in the wrong direction."
Discussing Salah specifically, Mourinho defended himself by insisting he was the one who talked Chelsea into going after Salah ahead of Liverpool.
He continued: "When people say I let Salah go, I say exactly the opposite. I bought Salah. I was the one who said 'buy that guy'. He was going from Basel to Liverpool, and I made a fight, I made a war, to make him come to Chelsea.
"Then comes the part when, to be a Chelsea player, you have to perform, or you need to wait. He didn't want to wait, he wanted to go on loan. And then Chelsea, at a certain point, decided to sell. He went to Fiorentina and Roma, and that was not me deciding to sell. I was saying let him go on loan if he feels he needs to play every minute of every game."
The now Roma boss added that he wasn't the one who 'pushed' either Salah or De Bruyne out of the club, instead putting the blame on the young players' impatience.
"When you are at Chelsea and you want to leave, go and another one comes," he said. "They were just kids who couldn't wait, and their careers say they were right, but it wasn't down to me. Probably other guys will say I pushed them out, but not them."
Somewhat in contrast to Mourinho's claims, Mikel John Obi recently told the same podcast how the Portuguese manager once reduced Salah to tears during a team talk.
The former Nigeria star Obi said: "He (Salah) was unlucky because Jose Mourinho, the manager at the time, didn't take any prisoners. It doesn't matter who you are, I remember a game away he had a go at Mo Salah at half-time and he was in tears, he was crying.
"We thought he was going to put him back on the pitch but he destroyed him and brought him off but that was his mentality back then.
"I don't think he would do that now, he has become more mature, he knows how to deal with younger players, that's how he got the best out of us then and that's why we were successful."
Since returning to England, Salah has gone on to win three Premier League Golden Boots and lift every major trophy available to Liverpool.
With his strike against Crystal Palace earlier this month, the Egypt captain reached 200 goals for the Reds – an amount if scored for Chelsea would make him comfortably the Blues second-top scorer of all time.