Dejean-Jones had 27 points, Niang added 26 with eight assists and 20th-ranked Iowa State never trailed in rolling past No. 18 Arkansas 95-77 on Thursday night.
Dustin Hogue scored 14 for the Cyclones (5-1), who led by as many as 23 points in extending their nonconference home winning streak to 24 games.
Iowa State's fast-break offense overwhelmed the Razorbacks (6-1) from the opening tip. The Cyclones took their first double-digit lead less than six minutes in and led 52-32 at the break.
Dejean-Jones led the way, shooting 8-of-8 from the floor and 4-of-4 from 3-point range.
"That's a pretty good line. I can't believe he missed a free throw. But it was everything," Iowa State coach Fred Hoiberg said. "He had to play good defense. He was out there the whole second half without a rest. ... It was great to see him get it going from the 3-point line."
Bobby Portis scored 19 to lead the Razorbacks, who haven't won a road game as a ranked team since 1999.
This was billed as potentially one of the highest-scoring games of the season. Arkansas entered ranked fourth nationally at 90 points per game, and Iowa State was averaging 83.4 points through five games.
The Razorbacks knew they were in trouble once they found themselves down 15 after 12 minutes -- even though they were shooting 50 percent from the field.
Iowa State pushed the tempo better than it had all season, and the Arkansas defense appeared powerless to stop the Cyclones.
Iowa State went on a 13-0 run midway through the first half to go up 39-20, and Niang's layup made it 48-26 with 2:26 left.
The Cyclones hit 18 of their first 28 shots -- with assists on 13 of their made baskets -- and nailed seven 3-pointers in the first 20 minutes.
"(Hoiberg) was preaching before the game that we really need to get out and step on these guys from the beginning," Niang said.
Portis hit a few shots early to keep Arkansas briefly within striking distance, and its press defense caused Iowa State some issues in the second half. But it was clear from the early stages that the Razorbacks were headed to their first loss of the season.
Alandise Harris had 15 points for Arkansas, which never got within single digits after halftime.
"We were a half-step slow. I thought they came out and they attacked us and they put us on our heels," Arkansas coach Mike Anderson said. "We got stagnant offensively."
Arkansas: Although Arkansas had visited Ames only once prior to Thursday, Anderson knows the Cyclones well. He went 8-2 against Iowa State as the coach at Missouri. ... The Razorbacks had assists on 14 of their first 16 shots -- yet trailed 61-38.
Iowa State: Niang was named to the Naismith Trophy watch list Wednesday. Niang averaged 18.2 points, 6.6 rebounds and three assists in Iowa State's first five games. He was even better against Arkansas, going 9-of-12 from the floor and 6-of-6 at the line.
Arkansas plays at Clemson on Sunday.
Iowa State hosts Missouri-Kansas City on Dec. 9.
Arkansas got within 11 twice late in the second half. But Niang answered with a bank shot off a hook and a drive from the 3-point line that featured two spin moves, and Iowa State went back ahead 81-68. Dejean-Jones then hit a contested 3 that made it 85-69 with 5:27 left.
Iowa State shot 64 percent from the field and outscored the Razorbacks by 20 points in the paint. Arkansas outrebounded Iowa State 9-2 on the offensive glass and 28-26 overall. The Razorbacks were held to a season low in points. They had 78 in a win over SMU.
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