The 21-year-old Guinean midfielder entered the field with six minutes to go, and immediately stole into the penalty area to score the only goal of the game and gift the newcomers their first top division win in their history. Not a bad way to announce himself to German fans who barely knew anything about him before the season started.

Leipzig were well aware of Keita's capabilities, of course. After all, he had been playing for Red Bull Salzburg for two seasons, and Ralf Rangnick -- the sporting director at both clubs -- originally signed him in 2014. There was a feeling, however, the midfielder was not be ready for the big time and the coach Ralph Hasenhuttl planned to introduce him gradually. A few magnificent minutes against Dortmund changed his mind completely, and it has been impossible to imagine Leipzig without the diminutive star ever since.

Keita didn't hide his ambitions. During the summer, he wasn't shy to claim: "I am looking forward to develop in the Bundesliga like Pierre-Emerick Aubameyang."

He has arguably accomplished that feat already, becoming the top player in Germany. Keita's average grade (2.54 out of six, where one is the highest mark and six the lowest) in Kicker is the best in the Bundesliga among outfield players. His contribution goes way beyond the four goals and five assists he has produced so far. He is everywhere on the pitch, both in attack and defence.

It would be hard to find a more complete midfielder in Europe these days, because Keita is an uncanny, almost unbelievable, mix of N'Golo Kante, Luka Modric and Franck Ribery.

On paper, he plays in a holding position at Leipzig, and very few midfielders make more tackles and interceptions than him. He is also responsible for building the play from behind with delightful through balls and wise distribution. All that doesn't stop him from bursting forward and taking on defenders. In fact, only Dortmund's Ousmane Dembele -- an out-and-out winger -- has completed more dribbles per game than Keita. With an average of 2.9, he leaves the likes of Ribery and Arjen Robben far behind.

Given such range of skills, it is easy to understand why he was nicknamed Deco in his homeland as a kid.

Naby Keita has helped propel unfancied Leipzig into title contention.

"Everyone thought that Naby is going to play for the biggest clubs in Europe," says Fode Kebe, who played alongside Keita at tiny FC Santoba. Bizarrely, his first trial in Europe, in 2011, ended in disappointment as Lorient didn't notice his potential. Two years later, the Guinean was back in France, and Le Mans -- where Didier Drogba started his career -- were keen to sign him, but went bankrupt before they could. Keita didn't give up and participated in an amateur tournament, where he was spotted by second division Istres.

He might have joined the club in November 2013, long after the season had started, but immediately became the key player, scoring and assisting on his debut. Supported on the field and in the dressing room by veteran former Marseille and Paris Saint Germain midfielder Jerome Leroy, 20 years his senior, Keita gained experience, and he is very grateful to his mentor. "Jerome gave me a lot of advice and taught me that it is necessary to work hard in order to fulfil my potential. I often think about that," the Guinean says.

Keita scored four goals and provided nine assists that term, but Istres were relegated to the third division and it was obvious that a big step forward was needed. Fiorentina, West Ham and Bordeaux were mentioned as possible suitors, but Salzburg acted faster.

The Austrians are known to have a keen eye for young prospects, and they were certainly not disappointed with the midfielder, who didn't hesitate to state he wanted to become the best African player. Sadio Mane, whom he met for a few weeks at Red Bull before the Senegalese star was sold to Southampton, was an inspiration for Keita. "He showed me the way," he said.

Keita was hugely instrumental in winning two championship titles, playing in different roles and excelling in all of them. He was positioned rather defensively in the 2014-15 season, but was given freedom to roam forward in 2015-16, which resulted in 12 goals and nine assists. Combining sublime technical skills and vision with tenacity and remarkable work rate, Naby became unstoppable. Even Jonathan Soriano, the club's top scorer, was certain: "Keita is our most important player."

The team had significant problems to replace him when the Guinean was ill with malaria in the beginning of 2016.

That illness might have cooled Arsenal's interest a bit, even though Arsene Wenger personally spoke to Keita in the summer. Manchester City and Liverpool were also reportedly interested, but the midfielder decided to move to Leipzig. "I didn't want to join a Champions League club immediately. It's still early," he said.

Little did he know that Leipzig are about to become a Champions League club themselves. The most disliked club in Germany are definitely doing things right on and off the pitch, and Rangnick has to take a lot of credit for cherry-picking anonymous talents and keeping faith in them. They might have lost at Bayern Munich in the big game in December, but came out of the winter break in superb form.

Naby Keita shares a similar indefatigability to Chelsea midfielder N'Golo Kante.

With star Swedish midfielder Emil Forsberg suspended, Keita became even more dominant. He set up Timo Werner's goal in the 3-0 thrashing of Eintracht Frankfurt with a sublime free kick, and then was involved in both goals as Leipzig condemned high flying Hoffenheim to their first defeat of the season.

Those performances prove that Keita can become even better, and Rangnick was absolutely right when he said: "Naby is showing more and more of his extraordinary abilities." He claimed so in November after the Guinean scored a magnificent goal at Freiburg with a long range shot. A few weeks before that, Keita scored a brace against Bremen -- the first after a breathtaking solo run and the second with a header. His versatility knows no bounds.

In his homeland, there are few doubts that Naby should become the greatest player Guinea have ever had. Former national coach Luis Fernandez, the ex-France star who knows something about midfield play, said: "Naby is strong and intelligent, he reminds me of Andres Iniesta."

That is the highest possible praise for the youngster, because the Barcelona star is his idol. Keita dreams of playing at Camp Nou one day, and at his current rate of progress those aspirations are realistic.