* Portuguese side finish third behind Zenit
* Garcia, Costa strike for Atletico in 2-0 win (Adds details, byline)
By Iain Rogers
MADRID, Dec 11 (Reuters) - Porto will have to settle for a place in Europe's second-tier club competition after their Champions League campaign ended with a 2-0 defeat at Group G winners Atletico Madrid on Wednesday.
Zenit St Petersburg lost 4-1 at Austria Vienna in the other match in the group but the Russians went through to the last 16 in second place as the first side ever to advance with six points from six matches, one more than Porto.
The Portuguese side's luck deserted them at Atletico's Calderon stadium as Josue had a penalty saved after Raul Garcia's 14th-minute opener and four efforts bounced away off the frame of the goal during the match.
Diego Costa made it 2-0 to Atletico in the 37th minute when he sped clear onto an Oliver Torres pass, rounded goalkeeper Helton and clipped the ball into the net.
Unbeaten Atletico finished the group stage with 16 points, with Zenit on six and Porto and Vienna on five. Porto qualified for the Europa League ahead of the Austrian side due to a superior head-to-head record.
"We had to focus on our match and win," Porto captain Lucho Gonzalez said in an interview with Spanish television broadcaster Canal Plus.
"But unfortunately we conceded some very naive goals and against a team like this you pay heavily for that," the Argentine added.
"We played well and created chances but sadly it wasn't our Champions League this time around and we were justly eliminated."
Needing victory to have any chance of progressing, Porto immediately went on the attack against a second-string Atletico and Jackson Martinez crashed a volley against the crossbar in the eighth minute.
Already assured of first place in the group, Atletico scored from their first genuine chance when Garcia controlled the ball on his thigh and lashed an angled shot into the net off the bar.
Porto came close to a leveller when a Silvestre Varela header bounced off the top of the bar in the 21st minute before Daniel Aranzubia felled Martinez in the area.
The Atletico reserve keeper atoned for his mistake by blocking Josue's tame effort but Porto continued pressing and a deflected Martinez shot hit the outside of a post in the 36th.
A minute later Costa doubled Atletico's lead and although Porto dominated the second half they were unable to breach an Atletico defence that has leaked only three goals in qualification.
"The way we have performed during the first part of the competition has been very good," Atletico coach Diego Simeone told Canal Plus.
"Porto had a few chances tonight but we hung in there and showed patience," added the Argentine, who has transformed the club into genuine contenders in La Liga and Europe since taking over at the end of 2011.
"Any opponent we get in the next round will be a challenge because otherwise they wouldn't have qualified," he said.
"We don't consider ourselves superior to any of the teams and it is definitely going to be very tough."
The draw for the last 16 is on Monday and Atletico's potential rivals are Arsenal, Manchester City, Bayer Leverkusen, Schalke 04, AC Milan, Galatasaray and Olympiakos Piraeus. (Editing by Tony Goodson)