The first half of the Group A clash was cagey, with the two sides creating very few clear-cut chances.
Then just after the half-hour mark Joao Moutinho's volley had little power and did not trouble Koval at all.
Koval was forced into making a brilliant save in the 35th minute, when he kept out a powerful header from Jackson Martínez.
Six minutes into the second half, Silvestre Varela could have put Porto in the lead when he latched on to a brilliant pass but failed to keep his shot on target from an excellent position.
Both sides went for the winner in the final 15 minutes of the match, with Lucho almost bagging a victory for Porto in the final moments with a shot that went narrowly wide.