The heat was won by Beijing gold medallist Michal Martikan.
The 33-year-old, from Slovakia, left it all to do in his second heat after missing a gate in his first run.
But he produced a near-perfect run of 90.56 to secure first place, ahead of the young Slovenian canoeist Benjamin Savsek, who set an early pace in his first run.
Afterwards, Martikan sought to play down his victory, saying: 'It means nothing because everything goes to zero for the semi-finals.'
In the K1, Germany's Hannes Aigner was well ahead of the rest of the field.
His second run of 83.49 was 3.58 faster than Spain's Samuel Hernanz's best effort.