Cristiano Ronaldo scored again as Portugal came from behind to beat Germany 2-1 in their Nations League semi-final.

The 40-year-old Ronaldo captained Portugal and scored his 137th international goal five minutes after substitute Francisco Conceicao equalised with a blistering shot in the 63rd minute on Wednesday (Thursday AEST).

Ronaldo became the oldest player to ever score against Germany, while ending his "curse" against the country. The former Real Madrid star had lost each of the previous five games he'd played against Germany.

Liverpool target Florian Wirtz had given the home team a 48th-minute lead with a perfectly placed header inside the right post, but Portugal coach Roberto Martínez made his changes count as he brought on Conceicao and Champions League winner Vitinha among the substitutes.

Vitinha excelled as Portugal finished the game in the ascendancy just four days after he helped Paris Saint-Germain win the Champions League final against Inter Milan in the same stadium.

Germany needed goalkeeper Marc-Andre ter Stegen at his best to prevent the visitors from scoring any more.

PSG wing backs Joao Neves and Nuno Mendes both started for Portugal, while Stuttgart forward Nick Woltemade started for his Germany debut.

Conceicao only needed five minutes to make a mark with a brilliant long-range strike inside the far post after he surged past Robin Gosens like he wasn't there. Mendes gave Ronaldo a simple finish five minutes after that.

"It could have been more," Mendes said.

France play Spain in Stuttgart on Thursday (Friday AEST) in the other semi-final.