5 things to know about Champions League Group G

MADRID (AP) Atletico Madrid has made a perfect start in both its Champions League and Spanish league campaigns, but that record will be under serious threat when the team visits Porto in Champions League Group G. Here are five things to know about Porto-Atletico and the other match in the group, Zenit St. Petersburg-Austria Vienna:

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NO TEARS NOW SHED FOR RADAMEL FALCAO

When Radamel Falcao left Atletico to join Monaco in one of the summer's biggest transfers, many fans thought they had lost the most clinical striker in world football. Now, he is hardly missed at all. His boots have been more than filled by Diego Costa, a Brazilian who has not only equaled Falcao's tally of eight goals in the first seven league matches, but earned Atletico a rare win at crosstown rival Real Madrid. Costa's perfectly timed goal on Saturday humbled Madrid 1-0 at the Santiago Bernabeu, sealing Atletico's first victory there in 14 years. However, Porto will be relieved that Costa will not make the trip to Portugal because he is serving a Champions League ban.

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A CLASH OF IBERIAN GIANTS

Like Atletico, former European champion Porto is unbeaten in its domestic league this season, with its undefeated run going back to January 2012. Porto has a two-point lead after six rounds this season as it pursues a fourth straight Portuguese title. The team's only hiccup came when it drew 2-2 away at Estoril at the start of the month. Coach Paulo Fonseca will likely field Brazil full back Maicon, who is returning to full fitness from an ankle injury, but Russian midfielder Marat Izmailov is absent for personal reasons.

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MORE TO ATLETICO THAN COSTA

One of the keys to Atletico's perfect start this season is Costa's partnership with midfielder Jorge "Koke" Resurreccion. Eleven of Costa's last 17 goals have come from assists by the 21-year-old Koke, who will instead be feeding passes to David Villa and Baptistao against Porto. Simeone will also be pleased to include in-form Belgian goalkeeper Thibaut Courtois, who appears to have recovered from a finger injury sustained in a goalmouth clash with Madrid winger Gareth Bale late in Saturday's match.

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AUSTRIA VIENNA NEEDS TO IMPROVE, AND QUICKLY

Austria Vienna, beaten 1-0 by Porto on its Champions League debut two weeks ago, has won only one of its last six matches, including an embarrassing 2-1 domestic cup defeat at the hands of a 6th-division amateur club. "The way we perform these days is just not good enough," Austria Vienna coach Nenad Bjelica said. "We need to be fresher and have to be fully focused against St. Petersburg." Last year's Austrian league champions, they have struggled for consistency this season and lost 1-0 to Admira Wacker on Saturday. Vienna has been dealt a blow ahead of the game with forward Marko Stankovic ruled out for a month with a calf injury.

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ZENIT TRUSTS IN HULK

Zenit comes to the match as Russian league leader above Spartak Moscow, which it beat 4-2 on Saturday, and having lost just once in its last 11 games. The Russian team's attack will once again be led by Brazil forward Hulk, who is in good form having scored seven times in nine matches so far this season. Striker Alexander Kerzhakov has added confidence by scoring his 208th career goal to top the all-time scoring leaders table in the league. "In terms of our physical shape, everything's all right," former Arsenal midfielder Andrei Arshavin said. "Zenit will be very strong (on Tuesday)."