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Haller was announced as a new Dortmund player six months ago, when he was billed as the Ruhr giants' next great line-leader, having completed a €31 million transfer from Dutch champions Ajax Amsterdam following a goal-laden spell in Amsterdam.
But his return to German football was halted by a diagnosis for testicular cancer in July, just days after his transfer was announced.
The Ivory Coast international underwent surgery and received therapy to aid his recovery, but he never lost his unswerving focus on making his competitive debut for his new club.
His wish came true last weekend, when he was introduced as a substitute just after the hour mark, with Dortmund being held 2-2 by Augsburg and struggling to get the upper hand.
Haller, who was wearing boots with "f--- cancer" written on the side, received an overpowering and emotional welcome from both sections of the 81,000 spectators, and he proved influential with Augsburg struggling to cope with his movement and physical presence.
"We had goosebumps before the game when Sebastien addressed the team before we left the dressing room," head coach Edin Terzic said after the match, won 4-3 by BVB. "Then the 62nd minute was a very special moment for him and his family, and also for us as a team and our fans. Everybody is very happy that he is back and we were proud to share that moment with him. That's the power of football."
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The 28-year-old looked sharp despite his absence -- perhaps unsurprising considering his recent hat-trick in a friendly against FC Basel -- and he will now look to make up for lost time at the Westfalenstadion.
"It's not just emotionally important that he's back, look at the qualities he has," Terzic said. "The way he holds the ball up, the way he links up moves and brings better positioned teammates into the game. Also for those reasons are we so happy to have him back."
Dortmund's victory took them up to 28 points after 16 matches in the German Bundesliga, seven behind league leaders Bayern Munich.
The Bavarians were held 1-1 by RB Leipzig as the German top flight returned after the World Cup, with Eric Maxim Choupo-Moting playing his first competitive game since Cameroon stunned Brazil in their final group game.
The forward, who had been in Ballon d'Or-winning form before the World Cup break, was on target after just 37 minutes, finishing from close range for his 12th club goal of the season.
The veteran, whose future at Bayern remains uncertain, has now had a hand in 13 goals in his past 10 matches for Munich.
Over in Italy, Osimhen's dominance over Italian defences would be almost monotonous were his performances not so exhilarating. This weekend, however, it was another Nigerian who stole the show in Serie A.
This weekend, he scored twice -- capitalising on a Wojciech Szczesny howler to net with a powerful drive, and then slamming home a header -- while also registering an assist, as Atalanta drew 3-3 at embattled Juventus.
The visitors may rue their inability to hold on to a victory, but that should take little away from a dazzling Lookman showing as he took his tally to 11 goals for the season -- behind only Osimhen in the goalscoring charts.
A case can be made that the Nigerian -- signed by Atalanta on the recommendation of head of recruitment Lee Congerton, who worked with Lookman at Leicester -- is the Serie A signing of the season so far.
He's only the fourth Atalanta player in history to hit double figures in his first 19 Serie A games at the club -- and the first since 1953 -- and is proving influential as La Dea chase a UEFA Champions League berth.
Osimhen, meanwhile, scored his 13th league goal of the season as Napoli won away at Salernitana for their third successive victory.
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In the Premier League, two African debutants caught the eye.
At Crystal Palace, David Ozoh made his first league appearance -- at the age of 17 years, eight months and 15 days -- in the 0-0 draw with Newcastle United.
Ozoh eclipsed another Nigerian -- George Ndah -- as the Eagles' youngest Premier League player in history; Ndah made his bow for the club in 1992, at the age of 17 years, 11 months and five days.
Ozoh, born in 2005, described his substitute appearance as "crazy" and a "dream come true" in an interview with Crystal Palace TV.
"It means a lot," the midfielder said. "You put in all the hard work for this moment. It's a dream come true. I can't believe it; it's honestly the best feeling ever.
"When I got told to warm-up, I was nervous; but when I got on, I felt good and obviously just tried to play it simple, make a few passes, and grow into the game.
"Honestly, coming on in this game was crazy. It was a game that we really wanted to win, and to be put on in this type of game shows how much trust the manager has in me, so I'm really pleased."
The 20-year-old -- one of the breakout stars of the first half of the Ligue 1 season -- moved to the Vitality Stadium in a £20 million deal, and required just 28 minutes to set up Jaidon Anthony and register his first Premier League assist.
Burkina Faso's Ouattara arrived on the South Coast soon after Bournemouth owner Bill Foley bought a stake in Lorient, with his signing set to herald a new era of partnership between the two clubs.