First round defeats to Jiri Lehecka and Lorenzo Musetti the last two years have left him disconsolate and the Aussie No.1 must have feared the worst when he started poorly against Diallo.
Fortunately his opponent was no better with breaks of serve littering the opening set, and once de Minaur shook off the hangover from reaching the final in s'Hertogenbosch at the weekend he eased to victory.
The No.1 seed will now meet another Canadian Denis Shapovalov, who beat British wildcard Dylan Pennington-Jones 6-4 4-6 7-6 (7-3)
"A pretty big challenge, by no means the most pretty match, today was all about surviving and advancing," said de Minaur.
Referring to fiancee Katie Boulter reaching the semi-final last week he added: "She's put the pressure on me to play well here at Queen's. We love a bit of healthy competition."
It was only in the first set tie-break the players found some spark bringing the crowd alive with a series of gripping points before the Australia came out on top.
Winning the set seemed to trigger a release in de Minaur who maintained the tie-break form to dominate the second stanza.
Diallo saved two match points serving at 2-5 but only delayed the inevitable, the world No.6 wrapping up a 7-6 (10-8) 6-3 victory with an ace.
Having come through qualifying Rinky Hijikata gained a good win against Chile's Alejandro Tabilo, 6-2 6-4. He will now play Lehecka or the man who defeated de Minaur in the Netherlands on Sunday, Poland's Kamil Majchrzak.
Third seed Jacub Mensik's Wimbledon preparations got off to a disappointing start as the big-serving 20-year-old was out-foxed by wily French left hander Adrian Mannarino, losing a marathon clash 5-7 7-6 (7-3) 7-6 (7-5).
Frenchman Corentin Moutet faces a heavy ATP fine after turning the air blue at Queen's in a shocking live BBC television interview.
Interviewer Jenny Drummond had to apologise to tea-time viewers after Moutet said the 'F' word seven times.
The 27-year-old had just beaten compatriot Giovanni Mpetshi Perricard over three sets. Asked about how Mpetshi Perricard saved a match point with a 228kph second serve, Moutet said: "When he hits me at 142, I was like f***!"
Despite the Drummond saying "no F-bombs please," the world No. 36 replied "F*** f*** f***!". The grinning Moutet then swore three further times before the interview was cut short.
There was disappointment for Australians in other Wimbledon warm-ups
In Nottingham Dane Sweeney lost 6-7 (16-18) 6-1 6-2 to Briton Jacob Fearnley
In Halle, Germany Alexei Popyrin lost 6-4 6-2 to Belgium's Raphael Collignon.
Nick Kyrgios did not even get on court having had to withdraw at short notice after sustaining an injury to his right knee during training ahead of his first-round match against Sunday's Stuttgart winner Ben Shelton.
Elsewhere in Halle Alexander Zverev needed three sets to win his first match since his French Open title while Paris finalist Flavio Cobolli and title holder Alexander Bublik crashed out.
Top seed Zverev overcame a second-set lapse has he won his first-round match 6-3 4-6 6-2 against Czech player Vit Kopriva.
But Cobolli lost lost his grass season opener, 6-2 7-6 (7-4) against American Frances Tiafoe. Bublik, the winner last year and in 2023, went out 7-6 (8-6) 6-1 against Italian Mattia Bellucci.
Brazilian teenager Joao Fonseca lost as well, 6-2 6-2 to world No. 59 Yannick Hanfmann but second seed Felix Auger-Aliassime defeated Nuno Borges 6-3 3-6 6-3.
with agencies
