The hosts were much the better side through the friendly clash at Cheonan Baekseok Stadium, and earned their triumph courtesy of first-half goals from Kim Min-woo and Nam Tae-hee.
Their strikes came in the space of five first-half minutes and knocked the stuffing out of the visitors, who struggled to gain a foothold in proceedings.
Paraguay did improve after the interval and forced a couple of saves out of Kim Jin-hyeon, but the South American nation were unable to claw their way back into the match as the home side ensured Stielike's tenure got off to a winning start.
The German had been appointed as South Korea's coach prior to matches against Venezuela and Uruguay last month, but was brought in too late to oversee those games.
Paraguay goalkeeper Antony Silva had to rush from his line to thwart Nam in the 14th minute as South Korea started the stronger.
Their dominance paid off 13 minutes later as Lee Chung-yong broke free down the right and his low cross found its way to Kim Min-woo, who was able to regain his balance, control the ball and slot home.
The second arrived five minutes later in very similar circumstances. This time it was Lee Yong who delivered the ball from the right flank, and Nam was on hand to apply a first-time finish.
Nestor Ortigoza had Paraguay's first effort of the game kept out by Kim Jin-hyeon, before Nam fired another warning shot over the crossbar from a tight angle in the 38th minute.
The visitors did provide a greater threat in the second half, Derlis Gonzalez forcing a flying save from Kim Jin-hyeon in the 52nd minute.
Silva kept out Cho Young-cheol with his legs as South Korea counter-attacked, while Kim Min-woo saw an effort disallowed for offside just before the hour mark.
Substitute Jorge Rojas saw his thumping drive beaten away at the near post as Paraguay attempted to force a way back into the match, but they were unable to conjure up any clear goalscoring opportunities as Stielike's men saw out the win.
