But the gamble paid off handsomely, with the South African quickly proving his credentials and stamping his mark.
Mosimane left Mamelodi Sundowns to take over from Swiss tactician Rene Weiler, who quit for personal reasons during a crucial stage of Ahly's season.
It was quite an unusual choice for Egypt and Africa's most decorated team, who have a tradition of hiring European coaches or, at a lesser frequency, Egyptian ones.
"We wanted a coach who has a large African experience because we were about to play the African Champions League semis," Ahly chairman Mahmoud El-Khatib said in a television interview in November.
"We wanted a coach who won titles and knows us well. He fitted all the criteria and also seemed willing to take the job. It didn't take much to complete the deal as we reached an agreement quickly,"
A former Bafana Bafana coach and an acclaimed winner, with a 2016 Champions League trophy and seven league titles under his belt with Sundowns, Mosimane became the first non-Egyptian African to take over at Ahly.
He has exceeded expectations since, winning several lucrative trophies including back-to-back African Champions League crowns and an Egypt Cup title, as well as guiding Ahly to a third-place finish at the FIFA Club World Cup.
Mosimane's Moments of joy
Ahly had already wrapped up the 2019-20 league title by the time Mosimane had arrived, but he still made an instant domestic impact by steering them to an Egypt Cup triumph.
However, his ultimate challenge when he took over was winning a long-awaited Champions League trophy, which Ahly had not won since 2013.
He duly delivered, and in the most emphatic manners, as Ahly scored a late winner to down perennial Cairo rivals Zamalek 2-1 in a match that was dubbed the "derby of the century", little more than a month after he was appointed.
He followed that up with a bronze medal at the Club World Cup last February after Ahly defeated Brazil's Palmeiras on penalties, marking their first ever victory over a South American champion in the annual tournament.
Ahly then beat Morocco's RS Berkane in the African Super Cup before sweeping to a second straight Champions League accolade in style, crushing South Africa's Kaizer Chiefs 3-0 in a one-sided final in July.
"I am very proud of my players; they have done a great job and deserve all the credit. They are making history, just like the generation of Abou-Treika," Mosimane said.
Consecutive setbacks and doubts
Despite his impressive start, Mosimane still came in for some criticism from Ahly's demanding supporters after losing two titles in less than a month.
A series of error-prone displays saw Ahly lose the league title to bitter foes Zamalek, having thrown away what looked a comfortable lead, before losing to Talae El-Geish on penalties in the Egyptian Super Cup.
His future with Ahly was thrown into doubt, especially after talks over a new deal broke down in October.
However, the club moved quickly to dispel any doubts over Mosimane's future.
"There are no differences with the coach. There is a mutual will to extend his stay and all what has been said about him wanting an excessive raise is untrue," El-Khatib said in November.
"We agreed to delay the contract talks for later. All what he asked for were just assurances over his future and protection against media campaigns, but I explained to him that he earned praise following his victories and that he should assume the blame when the team loses.
"That's Ahly, no matter how many things you have won, the fans and media won't get lenient on you at any defeats," El-Khatib added, although he also admitted that the criticism levelled at Mosimane was harsh.
Mosimane seems to have recovered his mojo as Ahly started this season by firing on all cylinders, winning their first six league games, which included an impressive 5-3 victory over Zamalek.
He switched to a 3-4-3 formation and devised his strategy around the talent of protégé Percy Tau, whom he brought from Premier League side Brighton Hove & Albion.
"I have been here for just a year. I believe I had more successes than failures. But I learnt a lot in this year about Egyptian football and I think I am better prepared now," Mosimane said.
He ended the year with another triumph as Ahly beat Morocco's Raja 6-5 on penalties to successfully defend their African Super Cup title, having scored a dramatic late equaliser to force a shootout.
Some stern challenges lie ahead in the new year, with Ahly dreaming big in the Club World Cup and looking to become the first ever team to win the Champions League for three straight times.
Should Mosimane realise this feat, he will go down in history as one of Ahly's best ever bosses.
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