And while he didn't leave the bench in the first half, he showed what he could do with 16 minutes in the second half.
Jankovic, a freshman from Mississauga, Ontario, dunked off a missed jumper by Laurence Bowers with 14:18 remaining, the first two of his season-high 14 points in the game.
That highlighted a 14-3 Missouri run to start the second half, which propelled the 12th-ranked Tigers to a 68-38 win over Tennessee State.
"He was huge," senior forward Alex Oriakhi said of Jankovic. "When he came into the game, I said, 'We need your energy.' And that's exactly what he gave us."
Jankovic says practice allows him to be ready to enter a game off the bench, no matter how long he's been sitting.
"That's my game sometimes. I find myself in practice trying my hardest, so when the game comes -- I'm going up against guys like Alex and Laurence (Bowers) in practice -- I'm ready."
Bowers scored 18 points and had 10 rebounds and Oriakhi added 15 points and 10 rebounds for Missouri (8-1), which defeated its second consecutive Ohio Valley Conference team following a 81-65 win Tuesday over Southeast Missouri State.
Both teams failed to make a basket for several-minute stretches in the first half, combining for 18 turnovers and 34.6 percent shooting from the field.
But Missouri regrouped during the break and went on a 14-3 run to start the second half.
Missouri led by at least nine the rest of the way, gradually extending its lead following an M.J. Rhett free throw that cut the deficit to 32-23 with 15:07 left.
Missouri coach Frank Haith said Saturday's 23-point first half was the result of poor execution.
"We want to get off to good starts," Haith said. "We've had some games where we've gotten off to good starts and we didn't finish well. So it's just a matter of putting together 40 minutes."
After making four of its first six shots from the field Saturday, Tennessee State made only 11 of its next 57 attempts.
It was a similar struggle from 3-point range, as Tennessee State started 3 of 5, but finished 6 of 24.
"We reverted back to our old ways, taking too many 3's," coach Travis Williams said. "I felt we settled for too many 3's. We normally would make certain shots and we didn't make those shots tonight."
Tennessee State, which was picked to finish second in the conference's East Division, has played eight of its first 10 games on the road.
Bowers and Oriakhi combined for all of Missouri's 23 points in the first half except for an Earnest Ross free throw with 4:01 remaining.
The Tigers endured stretches of 5:54 and 4:49 without scoring a basket in the first half and turned the ball over 11 times, yet managed to shoot 40 percent from the field to take a three-point lead at halftime.
Missouri also outrebounded Tennessee State 52-27 for the game and made 15 of 19 free throws. Tennessee State only attempted five, all in the second half, and made two.
Bowers is averaging 22.3 points in his past three games. Before scoring 26 in Tuesday, his career high was 23.
"He's been real consistent," Haith said. "And he's been our go-to guy thus far this season. But I do think we have a number of guys who can score. Guys who just have to continue to get comfortable."
No one exemplifies being more comfortable than Oriakhi, who earned his third double-double of the season, one better than all of last season at Connecticut.
The 6-foot-9, 255-pound forward says Haith's confidence in him has allowed his offensive game to grow.
Missouri extended its home winning streak against nonconference opponents to 71 games dating to the 2005-06 opener.
The team has nine days off before likely adding highly touted transfer Jabari Brown to its lineup. Brown, who played at Oregon, joined the Tigers after the first semester of last season.
"He will not start, I can tell you that," Haith said. "But he'll get some court time."