Bangladesh thrashed Zimbabwe by 123 runs on the Duckworth–Lewis–Stern method in Sylhet, sealing a 3-0 series triumph and making it 50 ODI wins from 88 matches as skipper for Mortaza.
The 36-year-old was then showered with effusive tributes from the likes of Liton Das, who scored a stunning 176 to set a new national record in the format.
"He's got a very special place in my heart," Das said of Mortaza. "I made my debut under him.
"He's always supported me. Having a captain like that is always rare.
"We will miss him, because when he leads, there's no distinction between seniors and juniors. It's a lot of fun."
Mortaza gave credit to his players, saying: "This is a great honour. My boys have been fantastic. They have given everything for the team. I'd like to say my thanks to all the boys."
Adding to the kind words, Mahmudullah cited Mortaza's overall impact on the game in Bangladesh.
"He's been a brother and a friend, and he's done so much for Bangladesh cricket," he said. "We have operated in a very nice way. When he took over, we were floundering a little bit."
They were sentiments echoed by Tamim Iqbal, who shared a 292-run opening stand with Das on Friday.
"When he took over in 2014, we were nowhere," said Tamim, after making an unbeaten 128. "From 2014 to 2019, he took us to a stage where we were taken seriously all over the world.
"There were people who wanted me dropped, but he backed me all the way."
Das' unbeaten 126 was the pinnacle of a ruthless batting performance from the hosts, whose top seven all scored 19 or above.
Opening with Tamim Iqbal (24), Das smashed 13 fours and two sixes off 105 balls as he recorded his second career ODI century before retiring from his innings, apparently having succumbed to the heat and humidity.
A half-century from Mohammad Mithun put paid to any hopes of a Bangladesh collapse, though, as Zimbabwe were set a target of 322.
Mohammad Saifuddin (2-33) found the stumps of Tinashe Kamunhukamwe with the fourth ball of the second over, and when Zimbabwe stumbled to 79-5, victory appeared unlikely.
Debutant Wesley Madhevere (35) made the chase somewhat respectable, but Tinotenda Mutombodzi edged Mashrafe Mortaza (2-35) to Saifuddin to hand Bangladesh victory by 169 runs, eclipsing their previous biggest winning margin in the format of 163, set against Sri Lanka in January 2018.
Mortaza also became only the fifth bowler to take 100 ODI wickets as a captain, a feat previously achieved by Wasim Akram, Shaun Pollock, Imran Khan and Jason Holder.
In a match shortened by rain to 43 overs per side in Sylhet, the hosts posted 322-3 in Mortaza's final game as skipper, with Das and Iqbal sharing a 292-run opening stand – the third highest in ODI history.
Zimbabwe were set a revised target of 342 and came up well short, Mortaza earning his 50th win in the format as the side's leader, the 36-year-old chipping in with 1-47 in a 123-run DLS triumph.
The home side were making fine headway when the weather closed in, the Tigers going off for more than two and a half hours with 182 runs on the board and the first pairing still going strong.
After resuming, Carl Mumba did manage to break the bond, taking three late wickets, although Tamim – who made 158 in the second match – remained unbeaten on 128.
Das smashed 16 fours and eight sixes in his stunning career-best 176, which came from 143 deliveries and ensured he eclipsed Tamim's tally from the previous outing to claim a national record in the format.
Zimbabwe's response was not nearly as spectacular, with Tinashe Kamunhukamwe falling in the first over to Mortaza and setting the tone for an innings of fruitless toil from the tourists.
Sikandar Raza did post a defiant 61, with Regis Chakabva (34) and Wesley Madhevere (42) also gaining some credit, but their contributions came in another losing effort as Mohammad Saifuddin (4-41) did most of the damage.
The result completed a miserable series for Zimbabwe, who lost the opener by a record 169 runs, before succumbing to a defeat by just four runs in the second meeting.
The 36-year-old paceman first led the Tigers in white-ball cricket back in 2014 and has gone on to skipper his country 87 times in the shortest format.
Mortaza will get the opportunity to end his reign with a 50th ODI victory as captain when Bangladesh go in search of a 3-0 whitewash at Sylhet.
"I am leaving the Bangladesh captaincy," Mortaza said in a press conference on Thursday. "The third ODI is going to be my last game as captain.
"I took the decision myself. As a player, I will keep trying to give my best if I get the opportunity. I wish the next captain all the best.
"I believe that the Bangladesh team will reach the next stage under him. I will try to give him all the support through my experience.
"I think the three available senior players each have the ability to lead the side. Hope the BCB takes the best one of them."
Mortaza, now a member of parliament in Bangladesh, added: "I am everything due to cricket. If I didn't finish playing cricket, I would have been doing fish farming.
"My future definitely includes cricket, and if a player requires me, I will give it my best. I have to do my work in my constituency until the next election."
