The 20-year-old - named Bote by birth, but after his father persistently called him Ridle, after Borussia Dortmund legend Karl-Heinz Riedle, the young star had his name officially changed when he was able - had only made one senior appearance this season, in a 3-1 DFB Cup win over VfB Stuttgart just before Christmas.
He was actually on his way to Freiburg to play for the reserves when he was hauled off the team bus and rerouted to the Opel Arena on Sunday, to be thrown in at the deep end against last season's Bundesliga runners-up.
"I found out at a motorway service station that I should get off the bus," Baku revealed to Sky Deutschland. "It took me 45 minutes to work out where I was, but in the end I got there and the fans were happy, my teammates were happy, I was happy."
On a day when the world's most powerful cars were charging around the streets of the Azerbaijani capital, it was perhaps fitting that Mainz unveiled a Formula 1 of their own in the shape of Baku. The turbo-charged midfielder ended up having a much greater impact on the game than his illustrious opposite number, Naby Keita, who was sent off in stoppage time.
Baku covered more ground than any of his teammates – seven miles – and completed a team-high 21 passes. He also clocked 86 runs – 30 more than Keita – and 34 sprints. More importantly, he capped off a perfect top-flight debut by firing in Mainz's third goal late on.
"A long ball came forward, I went for the second ball and took it with me perfectly," Baku explained to bundesliga.com. "I got past Upamecano with another touch and then put it in the far corner, just as I would in training!"
Watch: Baku talks us through his first Bundesliga goal
The Mainz native, who has been on the club's books since 2007, moved up to the reserves last summer – and his impressive performances in the Regionalliga soon caught the eye of first-team head coach Sandro Schwarz. While he is of Congolese origin, the diminutive (5'9") midfielder has already represented Germany at U18 and U19 level.
A central midfielder by trade, Baku has demonstrated his versatility this season by playing out wide, as a defensive midfielder and even at right-back. It was from the latter position that he scored his first goal for the reserves – against Kickers Offenbach – but his effort against Leipzig is likely to have a much greater ripple effect.
"I don't really know what to say!' he admitted after the final whistle. "It's unbelievable. Today couldn't have gone better for me."
Indeed, if his first Bundesliga game is anything to go by, you haven't heard the last of Ridle Baku.