The Serie A champions took control of the match through Dimarco, who opened the scoring in the 20th minute in front of 50,325 fans.
Andy Diouf then doubled Inter's advantage after the break before Juventus winger Francisco Conceicao gave his side hope with a late goal.
Dimarco has been one of Inter's standout players during their preparations for the new season. The 28-year-old had also scored in Wednesday's 1-1 draw with AC Milan at the same venue.
Inter started brightly and broke through when Dimarco finished from close range after Ange-Yoan Bonny delivered a dangerous cross.
Juventus goalkeeper Michele Di Gregorio then kept his side in the contest with several excellent saves as Inter began to take control.
Juventus struggled to turn their patient possession into clear chances, although Kenan Yildiz tried to provide a spark before half-time with a powerful effort from outside the box that missed the target.
Both teams made several changes during the second half, with Dimarco among those withdrawn after playing the full match against AC Milan.
Inter continued to press and were rewarded again in the 62nd minute. Diouf finished a well-worked move after receiving a precise pass from Pio Esposito to make it 2-0.
Juventus refused to give up and Conceicao produced the highlight of their late response when he found the net in the 85th minute.
However, Inter held on to secure another encouraging pre-season victory.
Juventus will finish their Perth schedule against Serie B side Palermo on August 11, while Inter will face Real Betis in Bari on August 15 in their final pre-season match.
The new Serie A season begins on August 22.
