Tied on three points apiece after last week's reverse fixture in Portugal, Group B rivals Bayer Leverkusen and Porto meet again on Wednesday, with progress to the Champions League's last-16 still up for grabs.
While surprise package Club Brugge are currently sprinting off into the distance, both sides join Atletico Madrid six points behind the leaders after Leverkusen lost 2-0 at Estadio Dragao last time out - a result which prompted a change of coach for Die Werkself.
Match preview
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Not unexpectedly, Leverkusen parted ways with former coach Gerardo Seoane after a slow start to the season continued with back-to-back defeats last week, and failing to take even a point home from Oporto proved to be the final straw for the club's board.
Eight losses in 12 games to that point did not make particularly pleasant reading - and represented their worst start since promotion to the German top flight back in 1979 - so with the team also stuck inside the Bundesliga drop zone, a new leader has been called upon to rejuvenate a talented squad.
Hotly-tipped as a managerial maestro of the future, Champions League-winner Xabi Alonso was swiftly appointed amid much fanfare in North Rhine-Westphalia, and the ex-Bayern Munich man has already made a significant impact.
On the Spanish star's debut in the dugout, his new side swept to a comprehensive 4-0 win over Schalke on Saturday, with speedy wing-back Jeremie Frimpong notching twice alongside forwards Moussa Diaby and Paulinho to secure just a second league victory of the campaign.
As Seoane led Leverkusen to a third-place finish last term - their best result since 2015 - and returned them to the Champions League group stage as a result, expectations are far higher than their current station at home and abroad.
Group B remains so finely-balanced from positions two to four, there remains every chance that they can still qualify for the knockout rounds, though, and home advantage could prove a crucial factor on Wednesday.
After Patrik Schick had a penalty saved in Portugal and Frimpong was sent off late on, Die Werkself's fourth loss from five away from home in the Champions League highlights their greater comfort on German soil. Indeed, they came out on top in their only previous home meeting with Porto - the first leg of a 5-2 aggregate win in the Europa League two years ago.
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After ending a four-game losing streak in the Champions League stretching back to last season, Porto's win on home soil not only got them off the mark in Group B but also puts them back in the mix for European football after the World Cup.
Nigerian full-back Zaidu Sanusi put the hosts ahead in the 69th minute last week, before Wenderson Galeno made sure of the result with an 86th-minute strike, and now victory in the reverse fixture would lift them above their latest opponents in the standings.
The Portuguese champions currently sit third in the Primeira Liga table, too, with only one defeat from their first nine games seeing them trail leaders Benfica by three points.
Since their shock 4-0 capitulation to Club Brugge on the second matchday, Sergio Conceicao's side have drawn with Estoril, then beaten Braga, Leverkusen and Portimonense, so will arrive in Germany in fairly good form.
The Dragons had failed to win either of their previous two away games before turning over the latter on Saturday, courtesy of strikes from Pepe and Otavio either side of half time, so Conceicao will be keen to repeat that result at the BayArena - albeit against much tougher opposition.
Team News
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One of Europe's most frequent dribblers from the full-back position so far this term, Jeremie Frimpong will be forced to miss Wednesday's match, after being dismissed in Portugal last week. Midfielder Robert Andrich also serves a suspension.
Leverkusen are set to be without Karim Bellarabi, Florian Wirtz and Exequiel Palacios through injury, while Iran international Sardar Azmoun joins them on the sidelines after suffering a calf muscle tear in the warm-up at Estadio Dragao.
For his first Champions League game as a coach, Xabi Alonso may therefore retain the front three he started on Saturday, which would see Moussa Diaby and Callum Hudson-Odoi flanking central striker Patrick Schick.
Meanwhile, Porto captain Pepe has picked up a knee injury in training which not only rules him out of action this week but also, potentially, out of the fast-approaching World Cup.
In the 39-year-old's absence, David Carmo and Fabio Cardoso should start at the centre of the visitors' back four, while Mehdi Taremi and Evanilson are likely to be paired up front.
Bayer Leverkusen possible starting lineup:
Hradecky; Tapsoba, Tah, Hincapie; Kossounou, Aranguiz, Demirbay, Bakker; Diaby, Schick, Hudson-Odoi
Porto possible starting lineup:
Costa; Mario, Cardoso, Carmo, Mario; Otavio, Uribe, Eustaquio, Pepe; Taremi, Evanilson
We say: Bayer Leverkusen 2-1 Porto
Revenge could be served lukewarm in Leverkusen, as the hosts will strike back just a week after their defeat at the Dragao. With an exciting new era afoot under highly-rated boss Xabi Alonso, optimism can ignite a performance to lift the hosts back above Porto in the standings.
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