VOLGOGRAD, Russia -- The possession football championed by coaches like Pep Guardiola is supposed to produce aesthetically-pleasing goals. Against strong defenses and world-class goalkeepers, sometimes you need to go back to basics.

This World Cup has started with a spate of goals off of set pieces and penalty kicks, as many teams have struggled to score in the run of play.

Inevitably, superstars Cristiano Ronaldo and Lionel Messi have been part of the story, on opposite sides.

Ronaldo’s delivered with artistry, curling in a free kick as part of a hat trick in Portugal’s draw with Spain. Ronaldo famously hones his kicks with long hours of training, using his trademark wide stance from all angles so he is ready for the moment on the big stage.

Ronaldo’s goal was one of three free kicks scored in the opening four days in Russia. That’s as many as the entire tournament in Brazil four years ago.

It started with Aleksandr Golovin arcing the ball into the net in Russia’s win against Saudi Arabia on the opening day . Aleksandar Kolarov scored on a free kick in Serbia’s win over Costa Rica on Sunday.

Months before he failed to stop Ronaldo’s free kick, Spain goalkeeper David de Gea was grumbling about the Adidas ball developed for the tournament, calling it "strange."

Egypt goalkeeper Essam El Hadary believes the ball-makers pander to the desires of outfield players.

"We are the victims of FIFA and the ever-developing football," he said Monday.

The official ball goes through rigorous tests before being approved by Switzerland-based scientists . The "Telstar 18" had to retain its shape even after being shot against a steel wall 2,000 times at 50 kilometers per hour in Empa’s laboratory.

"The deformation caused by the impacting foot initially gives the ball a somewhat wobbly movement," said Martin Camenzind of the laboratory for biomimetic membranes and textiles. "Experienced players take advantage of this effect and ‘Bend it like Beckham.’ This is not actually a matter of magic, but of applied physics."

And skill when striking the ball.

"This must be perfectly well-rehearsed, because as soon as the foot is on the ball for a few milliseconds, the player can no longer deliberately influence his movement," Camenzind said. "There is simply not enough time to direct nerve impulses from the foot to the brain and to send tactically sophisticated feedback to the muscles of the player. And so, in the brevity of the shot, the physics of foot and ball must fit perfectly."

You still have to pick a space in the net, something Messi struggles to do from penalties lately. Argentina teammates presented him with the opportunity to strike the winner against Iceland but the Barcelona forward failed for the fourth time in seventh penalty attempts for club and country.

Argentina was struggling to break down the tournament newcomers, and Messi knows scoring would have changed the match.

"They would have opened a little more and we could have found more spaces," Messi said.

The tactical script is following the trend from four years ago at a rapid pace. Eleven percent of all goals in Brazil came from corner kicks, while 18 of the 32 headed goals were from set pieces.

"The importance of set pieces has increased tremendously and every team used this tactic as a valuable attacking tool in their game," FIFA’s 2014 World Cup technical report concluded. "Defending teams tried to avoid any kind of free kick situations close to their penalty box, fully aware that they created danger. The vanishing spray also helped to ensure that there were no discussions, disruptions or encroachments at free kicks."

The new technology this time is VAR. Video assistant referees should ensure there are more free kicks, corners and penalties.

Video review gave Andreas Granqvist the platform to net from the spot for Sweden against South Korea on Monday as the number of penalties in Russia reached eight in 14 games. That is only two off the total in 48 group-stage fixtures in 2014.

Croatia benefited from a set-piece double in a 2-0 win over Nigeria: an own-goal coming from a corner and Luka Modric’s penalty.

"We worked hard on those elements on the training ground," Modric said.

There are no highlights of slick moves for the purists to pore over, but Croatia is top of its group ahead of Argentina.

"Corners and penalties are part and parcel of football," Dalic said. "It doesn’t matter how you score, what matters is you score. There was some luck there, but we earned our luck. Of course we want to be more efficient on attack, but we are not going to split hairs about the way we scored."

Nigeria coach Gernot Rohr knows what he has to work on before facing Iceland next.

"This was not a question of tactics," Rohr said. "We played with four in the back because there were three strikers and the Croatian strikers are very strong. What we were missing ... was to be more professional on set pieces."(AP)