Spain were held by Serbia in the UEFA Nations League in their first game since winning Euro 2024, while Cristiano Ronaldo reached another milestone by scoring his 900th career goal as Portugal beat Croatia.

Eight of Spain's starting line-up in their Euro 2024 final victory over England almost two months ago were on the field at kick-off against Serbia in Belgrade.

Among them was Lamine Yamal, with the Barcelona prodigy just one of the Spain players to be denied by home goalkeeper Predrag Rajkovic.

Luis de la Fuente's team are also the reigning Nations League champions having won the most recent edition of the tournament last year.

They will now hope to register their first victory in League A, Group 4 when they travel to face Switzerland in Geneva on Sunday.

The Swiss lost 2-0 to Denmark, with Patrick Dorgu and captain Pierre-Emile Hojbjerg scoring late goals for the home side in Copenhagen.

Switzerland finished the match with nine men as both Nico Elvedi and Granit Xhaka were sent off in the second half.

In Lisbon, Ronaldo's 900th career goal proved to be the winner as 2019 Nations League champions Portugal edged Croatia 2-1 in Group A1.

Ronaldo, 39, put behind him a disappointing Euro 2024 in which he failed to score as he turned in a Nuno Mendes cross in the 34th minute at the Estadio da Luz to reach the landmark.

He appeared emotional as he celebrated the goal, his 131st in a Portugal shirt. Half of his goals were scored for Real Madrid, with the remainder spread across his spells at Sporting Lisbon, Manchester United and current club Al-Nassr.

Diogo Dalot's goal had put Portugal in front early on before Ronaldo netted, with a Dalot own-goal reducing the deficit before the break.

Portugal next host Scotland, who lost 3-2 to Poland at Hampden Park, with the visitors grabbing the victory thanks to a 97th-minute Nicola Zalewski penalty.

Elsewhere, there were wins for Slovakia and Northern Ireland in League C, while Sweden -- now being coached by Jon Dahl Tomasson -- beat Azerbaijan 3-1 away in Baku with Newcastle United's Alexander Isak netting twice.

History was made in League D as San Marino, the world's worst team according to the FIFA rankings, beat Liechtenstein 1-0 to claim their first ever competitive win.

The tiny country of barely 30,000 people, surrounded by Italy, came into the match at their San Marino Stadium looking for a first win of any sort since beating Liechtenstein in a friendly in 2004.

Liechtenstein had a goal disallowed for a tight offside in the first half before San Marino pounced on a defensive error to grab the winner in the 53rd minute through Nicko Sensoli. (AFP)