* Poland to punish fans detained in fighting
* Germany and the Netherlands renew old rivalry
* Portugal risk early exit if they lose
KIEV, June 13 (Reuters) - Substitute Silvestre Varela smashed in a late goal to grab a 3-2 victory for Portugal over Denmark on Wednesday as a row brewed between Poland and Russia over clashes between their fans at Euro 2012.
Varela's 87th-minute strike secured all three points for Portugal in a pulsating match after Denmark had erased their two-goal lead with close-range headers by Nicklas Bendtner in the 41st and 80th minutes.
Victory in the Ukrainian city of Lviv put Portugal back in contention in Group B after they lost their first match to Germany, who were playing the Netherlands in Kharkiv.
Denmark also have three points in a tight group but could not reproduce the form that spurred them to a shock 1-0 victory over the Dutch.
Cristiano Ronaldo, the world's most expensive footballer, misfired in front of goal for Portugal but defender Pepe struck in the 24th minute with a powerful near-post header from a corner and striker Helder Postiga scored from close range in the 36th minute.
Off the pitch, tension was growing between Russia and Poland over fighting in which police fired rubber bullets and tear gas and detained 184 people before the countries' Group A match in Warsaw on Tuesday.
The Kremlin said President Vladimir Putin had told Polish Prime Minister Donald Tusk by telephone that Warsaw bore "full responsibility" for fans' safety and Russia's Foreign Ministry blamed the violence on Polish fans.
The clashes were an embarrassment for Poland, which had until Tuesday presided over a mostly peaceful tournament with co-hosts Ukraine, and Warsaw apologised for the violence.
Many Poles still resent decades of Soviet domination after World War Two and what they regard as Moscow's increasingly nationalistic tone.
Poland promised tough punishment over the clashes, which began as Russian fans marched towards the stadium before the match which ended 1-1. Masked groups attacked the Russians, some of whom fought back, and both battled the police.
Interior Minister Jacket Cichocki said the detained Russians would probably be expelled from Poland and banned from Europe's border-free Schneyer area for five years.
"When it comes to our hooligans, I hope the prosecutors and especially the courts will be strict," he said.
UEFA said it was determined the violence would not be repeated. A statement released by European soccer's governing body condemned the clashes but also implied that the police show of strength had been over the top.
"UEFA's philosophy is to create a welcoming environment coupled with a low-profile approach to policing," it said.
"UEFA is determined that the overwhelmingly peaceful and festive atmosphere that has so far pervaded UEFA Euro 2012 will be continued right up to and including the final in Kiev on Sunday July 1."
The clash between the Netherlands and Germany renewed an on-pitch rivalry that goes back to the emergence of the Dutch as a global football powerhouse in the 1970s, particularly after Germany's 2-1 final victory at the 1974 World Cup.
The 1990 World Cup round-of-16 win for the West Germans included an infamous incident where Dutchman Frank Rijkaard spat at German Rudy Vogeler and both players were sent off.
Germany coach Joachim Loew said the fractious encounters of the past had been replaced by a rivalry based on respect. But the stakes are high, particularly for the Dutch after their defeat by Denmark and another loss could seal their exit.
Although Germany are among the tournament favorites, team manager Oliver Bierhoff said they would be wary against the Dutch after being beaten in their second games in Euro 2008 and at the 2010 World Cup.
"I hope that after the second game this time it will be different and that we come out as winners," the former Germany international told reporters. (Editing by Ed Osmond)