The Peruvian international subsequently paid back Seattle Sounders with an even more important gift, scoring the lone goal in a 1-0 road victory against San Jose Earthquakes on Wednesday night.
Ruidíaz took a cross from Cristian Roldan at the top of the penalty box, took one touch, and then volleyed the ball past diving San Jose goalkeeper Andrew Tarbell and into the lower left corner of the net in the 62nd minute.
Goalkeeper Stefan Frei made five saves to post the shutout, and Sounders (6-5-9, 23 points) remained unbeaten in five matches this month (3-2-0) as the two-time defending Western Conference champions attempt to make another late-season rally.
Earthquakes (2-6-12, 12 points) saw their winless streak reach 11 matches (0-4-7).
Ruidíaz, the Liga MX leading scorer each of the past two seasons for Morelia, was acquired during the international signing period and made his debut for Sounders as a reserve last weekend against Vancouver.
He nearly made an immediate impact on Wednesday, striking a 14-metre shot just wide of the left post in the opening minute for a Sounders team that has scored a league-low 19 goals this season.
Earthquakes had two players making their MLS debuts: defender Guram Kashia, 31, a Georgian national and former captain of Dutch side Vitesse, and midfielder Luis Felipe Fernandes, 22. Fernandes was issued a yellow card in the 38th minute for unsporting behavior after fouling Sounders midfielder Nicolás Lodeiro.
The teams combined for 12 shots in a scoreless first half, but only three of those found the target.
Sounders had an opportunity in the 20th minute as Lodeiro crossed a ball from the right wing for Harry Shipp in the middle of the penalty box. The ball found its way to Ruidíaz near the far post, but Tarbell quickly charged off his line to knock it away from Ruidíaz before he could get set for a shot.
San Jose’s Valeri Qazaishvili attempted a curling shot with the outside of his right foot from 16 metres out in the 40th minute, but Frei made a sliding stop on it near the far post.