On Sunday, in the blur of an 80-yard touchdown run, he showed them what they missed.
The sixth-round draft pick from Clemson, starting because Rashard Mendenhall was out with an injured toe, rushed for 154 yards on 15 carries and the Arizona Cardinals intercepted four of Matt Ryan's passes in a 27-13 victory over the Atlanta Falcons.
Ellington's big run, tied for third-longest in Cardinals history, was part of a 21-point second quarter that put Arizona (4-4) in control for good.
"I was able to have a little speed burst out there," he said.
Fitzgerald caught four passes for 48 yards and a touchdown, in the process becoming the youngest player - at 30 years, 57 days - in NFL history to reach 800 career receptions.
Ryan had thrown three interceptions total in the first six games of the season for the Falcons (2-5). Rashad Johnson had two of Arizona's interceptions.
"I think we definitely had him confused," said Cardinals rookie Tyrann Mathieu, who had one of the interceptions. "Watching film, he has a tendency when he gets pressure to just throw the ball up there."
The Falcons were without wide receiver Roddy White for the second week in a row with ankle and hamstring issues. Atlanta also didn't have starting left tackle Sam Baker with a knee injury.
Arians traced his team's performance to Monday's practice, an extra workout that followed a Thursday night loss to Seattle.
"This game was won on Monday when I asked the team to come out in pads and we had a training camp practice," he said. "A lot of teams would balk at that, but our leadership and our veterans, we had the best practice we had all year and it set the tempo for this game and I think set the tempo for the rest of the season."
After throwing his 14th interception of the season, Carson Palmer had two TD passes, 10 yards to Fitzgerald and 15 yards to Floyd.
Steven Jackson, back for the first time since being sidelined with a hamstring injury in Week 2, managed just 6 yards on 11 carries.
With no running game, it was up to Ryan, who completed 34 of a season-high 61 attempts for 301 yards and a touchdown. He was sacked four times. Harry Douglas had 12 catches for 121 yards.
Asante Samuel's 51st career interception set up Matt Bryant's 24-yard field goal that put Atlanta up 3-0.
The Cardinals took the kickoff and Palmer threw 51 yards to Teddy Williams, a speedster who had signed with Arizona on Tuesday. Williams, who didn't play college football, played in seven games for Indianapolis last season on special teams and as a defensive back.
That set up Palmer's 10-yard TD pass to Fitzgerald on the first play of the second quarter and Arizona led 7-3.
Atlanta used up 7:17 on a 15-play drive but had to settle for Bryant's 30-yard field goal to cut the lead to 7-6.
"Those things come back to haunt you," Ryan said, "and they certainly came back to haunt us today."
On the first play after Atlanta's second field goal, Ellington followed blockers through the left side of the line, then burst outside and raced the length of the field for the touchdown, putting Arizona up 14-6 with 7:25 left in the half.
"We had an opportunity to hit the guy in the backfield, and then it popped out," Atlanta coach Larry Smith said. "Once we lost leverage, we weren't going to catch that guy. We said that he was going to be a potential game-wrecker going into this ball game."
Palmer threw 20 yards to Fitzgerald and Desmond Trufant was called for a facemask, moving the ball to the 35. Stepfan Taylor broke a pair of tackles on a 15-yard run to the 17. Two plays later, Palmer threw 15 yards to Floyd for the touchdown and Arizona led 21-6 with 1:52 left in the half.
Notes: In Cardinals history, the only runs longer than Ellington's 80-yarder were 83 yards by John David Crow in 1958 and Elmer Angsman in 1949. ... A black cat ran across the field just before kickoff. During the national anthem, security personnel corralled the cat and a guard carefully carried it off the field. ... Ex-Falcon John Abraham, who had a sack, left the game in the second half after a blow to the head but said after the game he thought he was all right. ... The previous youngest player to reach 800 catches was Jason Witten at 30 years, 238 days.
Copyright 2013 by The Associated Press