Krstic scored 14 points and had 10 rebounds, Milos Teodosic added 19 points and Novica Velickovic contributed 18 points and nine rebounds for Serbia, which clinched a place in the single-elimination round.
Krstic missed Serbia's first three games and Teodosic two because of suspensions over their role in a pre-championship brawl in Greece.
Australia pulled within three with 2:07 remaining in the game on Matt Nielsen's 3-pointer, but Teodosic and Velickovic then took over to secure Serbia's victory in Group A.
Teodosic nailed a 3-pointer and made two free throws, Velickovic made 3 of 4 free throws and Nenad Bjelica scored Serbia's last five points.
Brad Newley had 13 points for Australia and Patty Mills added 12.
"Our first objective was to stop their transition game and not give them easy baskets," Serbia coach Dusan Ivkovic said. "The second objective was to stop their inside game. We were partially successful in the first objective and completely successful in the second."
Serbia made 14 of 35 3-point attempts and went 16-for-31 from the 2-point range.
"We were back at full roster and that was a big help. We have a lot of respect for Australia," backup center Kosta Perovic said.
Serbia goes against top-ranked Argentina in the last group game on Thursday.
"It's a great opportunity to play against a team that has given so much to world basketball in the last 10 years," Ivkovic said. "We need games like this, my young team has the future in front of it. We don't really care what place we finish in the group."