It was the U.S. squad's first win in three games under interim coach Dave Sarachan.
Weah, the 18-year-old son of Liberian president and 1995 FIFA Player of the Year George Weah, entered in the 86th minute and was pulled down three minutes later by Derlin Gonzalez. Weah made his debut for Paris Saint-Germain on March 3, less than two weeks after his birthday, and the midfielder became the first player born in the 2000s to play for the U.S. national team.
Midfielder Marky Delgado and forward Andrija Novakovich also made their U.S. debuts. Sarachan has given three players debuts in each game since taking over for Bruce Arena, who quit in November after the U.S. failed to qualify for the World Cup.
Delgado's 50-yard pass led to the foul that resulted in the 45th-minute penalty kick.
Jorge Villafana won Bruno Valdez's throw-in deep in the U.S. end and headed the ball Tyler Adams. He squared it to Delgado before taking off. Adams reached Delgado's pass about 30 yards from goal and rounded goalkeeper Roberto Fernandez, who tripped him with an outstretched arm .
Wood coaxed Fernandez into diving right while his penalty kick went left for his 11th international goal. Wood was making his first start since Feb. 10, for Hamburg against Borussia Dortmund.
Novakovich replaced Wood in the 77th minute and missed a chance to score in stoppage time when his point-blank shot went into Fernandez' chest.
Sarachan is likely to add some veterans when the U.S. gathers in late May for exhibitions against Bolivia, Ireland and France. The Americans won't play a competitive match until the 2019 CONCACAF Gold Cup, and a new coach may not be hired until after this summer's World Cup.
The U.S. debuted new uniforms with blue horizontal stripes - which would have been their road set during the World Cup.
Sarachan started seven players with five international appearances or fewer, a youth movement that followed the end of the United States' streak of seven straight World Cup appearances.
A couple American Outlaws in from Sanford for tonight’s USMNT friendly vs Paraguay pic.twitter.com/hWf1dnFAbl— Mark Armstrong (@ArmstrongABC11) March 27, 2018
Zack Steffen started in goal after making his debut in the second half of a January exhibition against Bosnia-Herzegovina that ended 0-0.
Kenny Saief, playing for the first time since his debut last June, had a chance in the 16th minute when his 8-yard shot was deflected by Bruno Valdez with a slide tackle and cleared by Gustavo Gomez.
Paraguay, which is missing its second straight World Cup after four consecutive appearances, had a prime scoring chance in the 68th minute. Atlanta midfielder Miguel Almiron missed wide in the 68th minute and Hernan Perez was just off the target with a header in the 75th minute.
Paraguay: Roberto Fernandez; Junior Alonso, Gustavo Gomez, Fabian Balbuena, Bruno Valdez; Cristian Riveros (Richard Ortiz, 65th), Rodrigo Rojas (Derlis Gonzalez, 83rd), Nestor Camacho (Hernan Perez, 54th), Oscar Romero (Cecilio Dominguez, 80th), Miguel Almiron; Federico Santander
United States: Zack Steffen; DeAndre Yedlin, Matt Miazga, Cameron Carter-Vickers, Jorge Villafana; Wil Trapp, Mark Delgado (Tim Weah, 86th), Tyler Adams, Darlington Nagbe (Cristian Roldan, 90th+2), Kenny Saief (Rubio Rubin, 67th); Bobby Wood (Andrija Novakovich, 77th)