St.Petersburg, Feb 26 (IANS): The 2013 UEFA Champions League finalists Borussia Dortmund begun the knockout phase of the 2014 edition with a 4-2 away win over Russian club Zenit here.

Two Dortmund goals in the first five minutes gave the underdogs Zenit an enormous mountain to climb in the remainder of the round-of-16 tie Tuesday night, reports Xinhua.

A 2-0 halftime scoreline offered little for the home fans to cheer about, before an Oleg Shatov goal just before the hour gave Zenit a much-needed second wind.

A swift reply from star Dortmund striker Robert Lewandowski extended the lead to 3-1 and silenced the home fans once more, before Zenit's star striker Hulk rocketed a controversially awarded penalty into the top right corner of the net to narrow the German club's lead to 3-2 in the 69th minute.

Lewandowski was on hand in the 71st minute, however, to restore the two-goal lead almost immediately. A spate of late substitutions proved unable to alter the final scoreline.

Zenit now face an uphill battle to stay alive in this year's Champions League, and will need to record an unlikely away win by three goals or more in the return leg in Dortmund March 19.