What you might have missed: Mertens on fire for Napoli, Siem de Jong haunts Ajax

A busy weekend of action across Europe saw Manchester City beat Arsenal after going a goal down, while Lionel Messi led the way for Barcelona with a sublime showing against Espanyol in the Catalan derby.

Elsewhere, Juventus dealt Roma's Serie A title chances a major blow with a big 1-0 home win, and RB Leipzig and Bayern Munich are still battling it out for top spot in the Bundesliga ahead of the mid-season break.

But plenty of headlines were made beyond Europe's biggest clubs. Here are some things you might have missed over the weekend in world football.

DRIES MERTENS ON FIRE FOR NAPOLI

Napoli appeared to be in serious trouble when they lost Arkadiusz Milik to a serious knee injury earlier this season, having previously seen Gonzalo Higuain depart for domestic rivals Juventus.

Dries Mertens has started to pick up the goalscoring burden, though. The Belgium winger scored a hat-trick in last week's 5-0 battering of Cagliari and went one better with a four-goal haul in the 5-3 thriller against Torino, his fourth - a delicious lob - a particular highlight.

Mertens' goalscoring heroics saw him become the first player in over 42 years to score a hat-trick in consecutive Serie A games, and the first since Opta started collating data in 1994-95.

SIEM DE JONG COMES BACK TO HAUNT AJAX

A fortnight ago, Siem de Jong was jeered by his own fans twice within one week following an unimpressive start to life at PSV.

But the Newcastle United loanee has started to endear himself the fans in Eindhoven, starting by opening his account with the winner against Go Ahead Eagles last week.

And he made it two in two games when he netted an important equaliser against his former team Ajax.

The Amsterdam side turned down De Jong when he approached them during the close-season and they might regret that decision following Sunday's encounter at the Amsterdam ArenA.

MARSEILLE MARCH ON

After an underwhelming 2015-16 campaign and an equally difficult start to this season, Marseille opted to replace head coach Franck Passi with Rudi Garcia.

The former Roma boss endured a rough return to Ligue 1 with just two points from his first three games in charge, but they have started to turn the corner in recent weeks.

Marseille beat Lille 2-0 at the weekend courtesy of second-half goals from Bafetimbi Gomis and Florian Thauvin to climb to sixth place in the table with 27 points from 18 games.

Their third win on the trot represents their best run since May 2015, when they won four games in a row.

BESIKTAS UNBEATEN RUN COMES TO ABRUPT END

Much has been said about Real Madrid and Hoffenheim's unbeaten start to the season, but Besiktas' impressive run of results in the 2016-17 campaign has gone largely unnoticed.

The Istanbul giants collected 32 points from their opening 14 fixtures, winning nine and drawing the remaining five.

Nevertheless, Besiktas' superb run came to an abrupt end at the weekend when Kasimpasa sent them home with a 2-1 defeat, a Gokhan Gonul own goal condemning his own team to their first defeat.

Saturday's defeat saw them drop to second place in the table again, three points behind still unbeaten Basaksehir.

GALLARDO READY TO WALK OUT ON CUP WINNERS RIVER PLATE

Having led River Plate to Copa Argentina glory with a hard-fought 4-3 win over Rosario Central, Marcelo Gallardo has suggested he might walk away from the Buenos Aires side.

River have not always been at their best in the league, though, leading to criticism of Gallardo and the former midfielder will take a few days to think his position through before taking a decision on his future.

"I am going to take stock of what has happened and what is coming. I will have to analyse some things," Gallardo told Ole.

"I think it is only normal that I take three or four days to reflect. But I have not said I am leaving.

"Our main objective was to qualify for the Copa Libertadores and we achieved that. I thank the fans for the affection shown."