It was a bitter blow: the Spaniard had run competitively inside the top 10 for his whole race and looked destined to claim a well-deserved seventh position at the chequer.
Despite the loss of power, Ricciardo maintained a one-second lead over the Ferrari for the majority of the race - safe in the knowledge that the vehicle behind requires a significant pace advantage to make an overtaking move stick at Monaco.
Alonso, of McLaren, was only echoing what championship leader and defending champion Hamilton had said after finishing third behind Ricciardo and fellow four-time champion German Sebastian Vettel of Ferrari.
After the race, the British driver praised Ricciardo for his work over the weekend but didn't seem particularly pleased with his own performance.
"This is two years in the making so I finally feel like the redemption has arrived".
We highlight some of the best and worse moments of the race.
"He reported a sudden loss of power, and the engine guys could see from the data that the MGU-K had stopped completely", said Horner.
"We got home just using six gears".
"The problems threw a lot of doubt in my mind for a few laps", said Ricciardo after his second win of 2018.
It was soon time for his typical showmanship. It became clear in the opening stint that he had the faster vehicle, and once he built a two-second buffer on Vettel it looked as though he would control the race from the front. We had to survive with that problem all race. "But Daniel had the answers all the time". "Keep it focused." "Yeh - but I've got no power though", he replied with 48 laps of the 78 to go.
"It's just insane how little I was pushing, the least that I can ever remember".
"Firstly a big congratulations to Daniel and Red Bull", Hamilton said. He immediately fell into the clutches of Vettel, who went into full-on attack mode. Verstappen is next with just 35 points. He sustained damage to his front wing and right front tire, while the suspension was broken.
Even his team's engineer was amazed by his skill of driving. It was yet another mistake from the Kiwi in what is becoming a run of missed opportunities for the Le Mans victor.
Leclerc suffered a failure on his Sauber as he trailed the Kiwi with a handful of laps remaining but couldn't stop and plowed straight into the Toro Rosso.
"I mean I was 10 seconds behind and I was really conflicted, I am still in my heart, I still want to win this race, maybe something drastic is going to happen in the coming laps, so who knows, maybe the genius strategists might pull something out of the bag".