The marquee striker missed several clear-cut chances during the FFA Cup quarter-final match, which almost resulted in the Wanderers falling victim to one of the shock defeats of the tournament's short history.

They required a penalty shootout to avoid being dumped out by the state league club after settling for a 2-2 draw after extra-time. Riera missed several chances that would have given the Wanderers a comfortable victory.

While his movement, positioning and combination with other attackers was highly impressive, Riera's finishing was a sore topic for the Wanderers' coach.

Popovic was left bemoaning the Spaniard's failure to convert 14 attempts on goal over 120 minutes of football, four of which were on target.

Blacktown City goalkeeper Tristan Prendergast pulled off a number of fine saves to deny Riera, while the woodwork thwarted the Wanderers' striker on another occasion.

Riera made some amends for those errors with a dramatic equaliser in the 111th minute, as well as slotting the winning penalty, both after converting the first goal from the spot in the third minute.

Popovic admits Riera's misfortune in front of goal made for a frustrating affair, but says there is plenty of time for his prized recruit to polish his finishing before the start of the A-League season.

"Yeah, look I'm disappointed a bit. I think he should have had several goals tonight and we have time to still work on that. But the key thing is he got into great positions," Popovic said.

While, for the most part, Riera seemed luckless in front of goal during open play, he further endeared himself to his new fans with an industrious display off the ball.

The centre-forward regularly dropped deep into the midfield to win back possession, and even earned a yellow card for a foul that broke up an attack in his own half.

That work rate did not wane after 90 minutes, and a tireless performance in defence during extra time - as well his attitude towards teammates - drew plaudits from his coach.

"He's a worker, you can see how he's running even in extra-time there in the end. He got two goals and he got the winning penalty," Popovic said. "He showed that throughout, he's really encouraging in extra time and in the penalty shootout, that we can't change what's happened, we can only deal with what's in front of us."

While the Wanderers were made to work far harder than predicted against Blacktown, Popovic was delighted with the response from his players and their composure from the spot after an emotionally and physically draining 120 minutes.

"In the end it was our character that got us through. At 2-1 down in extra time, we had three or four boys cramping, very fatigued, and they had to show the spirit to come back in extra time and also the composure to take the penalties," Popovic said.

The Wanderers coach does not believe his players were complacent in facing a semi-professional team who had not played a competitive match in almost a month, but says an early penalty awarded in his team's favour lured them into a comfort zone.

"Maybe that goal relaxed us too much and, as the half wore on, we had numerous chances but you could just see them starting to get back into the game," Popovic said.