The Derby centre-back became his country's youngest international at 17 years and 195 days, and played a key role in keeping a skilful Paraguay out.
Wales goalkeepers Paul Jones and Lewis Price were also impressive in denying the likes of Haedo Valdez.
Ryan Giggs and Craig Bellamy created up front, but lacked the killer finish.
Wales manager John Toshack played his favoured 3-5-2 formation in front of a poor Millennium Stadium crowd of 12,324.
Giggs could have put the home side ahead in the first minute, the ball falling to him out wide after Paraguay keeper Justo Villar deserted his goal.
The skipper tried a long-range chip but fluffed the effort badly, while Bellamy also wasted a fine chance after being put clear by Jason Koumas.
It was the South Americans whose single-touch moves were creating chaos, keeper Jones - a surprise starter ahead of Price - making a fine snap save to deny Valdez.
The QPR veteran was on hand again with a double effort to keep out first the impressive Valdez and then the follow-up from Denis Caniza.
Straight after the break Giggs delivered a sublime through-ball to Koumas, whose surging run ended with a shot that flew just wide.
Giggs then freed strike-partner Bellamy, who saw Villar save his shot with his feet.
The visitors again showed a cutting edge - of which England will need to beware in the group stages of the World Cup - Cesar Ramirez turning James Collins to fire in a shot, and Humberto Paredes going close from the resultant corner.
Both were denied by the outstanding Jones, but immediately afterwards he was taken off to give youngster Price a run-out.
The game petered out with a flurry of substitutions from both sides, Wales bringing on even more youth in the form of Andrew Crofts, Joe Ledley and David Cotterill.
In injury time, Price saved superbly at the feet of Roberto Acuna, then, with Giggs and Koumas off, Collins went wide with a free-kick on the edge of the box.
Wales: Paul Jones (Price 66), Edwards, Ricketts, Gabbidon, James Collins, Nyatanga, Fletcher (Robinson 75), Bellamy (Earnshaw 78), Koumas (Ledley 70), Davies (Crofts 76), Giggs (Cotterill 86).
Subs Not Used: Partridge, Danny Collins, Weston.
Paraguay: Villar, Juan Caceres, Toledo, Caniza, Da Silva, Paredes, Ramirez (Cabanas 77), Barreto, Dos Santos (Riveros 67), Acuna, Haedo Valdez (Cardozo 71).
Subs Not Used: Gomez, Julio Cesar Caceres, Nunez, Fretes, Manzur, Gavilan.
Att: 12,324
Ref: D McDonald (Scotland).
