The City midfielder – who helped her nation win the inaugural tournament in 2020 - played the full 90 minutes for Pedro Martinez Losa’s side and had a hand in the game’s opening goal.
Weir stroked a delightful cross-field ball over to former City forward Jane Ross, with the ball eventually headed home by Lana Clelland on the stroke of half-time in Spain.
But Wales responded almost instantly before the break when Kayleigh Green was brought down inside the box by Jenna Clark after latching onto an aerial ball.
Jess Fishlock made no mistake from the spot, and then completed her brace just eight minutes after the restart smashing an effort in from close-range after a clever drag-back by Natasha Harding.
And ex-City forward Harding turned from provider to scorer on the hour, flicking home at the near-post to complete a swift Wales counter.
Weir and co. are now competing for fifth place in the Pinatar Cup and will face either Slovakia or Belgium on Saturday in their next fixture.
Meanwhile, Julie Blakstad was also in action as Norway were beaten 2-0 by host nation Portugal in the Algarve Cup.
The City midfielder played the full 90 minutes for her home nation, who reached the semi-finals of the previous tournament in 2020.
However, their campaign got off to a slow start this time round with goals in either half from Tatiana Ferreira and Carolina Mendes consigning the Scandinavians to defeat.
Blakstad and co. will face Italy on Sunday 20 February as they aim for a top two finish in the group stages.
