And then reality hit. Pirates pitcher Charlie Morton had the ball go off his glove, and he had to track it back down before he could make a throw to first.
Arenado lunged toward the first-base bag. It was too little, too late for salvation.
Arenado was out -- at first base and the game.
What once was a promising season has turned into a nightmare the last 7 1/2 weeks, and to see a young player with as much ability as Arenado short-change himself pushed manager Walt Weiss to the breaking point.
Colorado may have been nurturing a 1-0 lead at the time, and Arenado may be a Gold Glove fielder in addition to the No. 5 hitter in the lineup, but Weiss wasn't making any concessions to a scoreboard.
It was time to make a point. When the fourth inning ended, so did Arenado's night of work. Charlie Culberson took over at third base in the top of the fifth.
The Rockies wound up winning the game, 8-1, but they are still on a pace at 42-60 for the second-worst season in franchise history, and they are in the midst of a 16-40 slide that has taken them from three games out in the NL West to the worst record in the NL and a 14 1/2-game deficit to the division-leading Giants.
There are things like injuries, hitting slumps and pitching struggles that Weiss can't control.
Effort, however, is another topic, and Weiss made that clear with Arenado on Friday night.
"We talk about playing the game hard," said Weiss, "playing the game right and how important that is. Especially when you have been getting your [tail] kicked for a while, it's even more important, it's imperative.
"I didn't feel Nolan met that standard at that point."
"Nolan is a great kid, a great player," Weiss added. "That's how I saw it."
By the time the media was allowed into Colorado's clubhouse, Arenado was dressed and gone. He did, however, return to the bench for the remaining innings of the game, and he offered his sincere congratulations to the likes of Josh Rutledge, who doubled twice and drove in four runs, and Carlos Gonzalez, whose 10th home run punctuated a seven-run seventh.
"He knows what he did wrong," said shortstop Troy Tulowitzki, who became a confidant of Arenado's when Arenado was at the Class A level in the Minor Leagues. "Like all of us do, we make a mistake and learn from it. He's going to learn from his mistake."
Arenado has proven that before. It was back in the summer of 2012. He was playing with Double-A Tulsa, and he had enjoyed that previous offseason by earning Arizona Fall League MVP honors over a group that included Mike Trout. Arenado was just waiting for a phone call to tell him he was jumping directly to the big leagues.
It never came.
There were concerns about his attitude and focus.
General manager Dan O'Dowd even made a late July trip to Tulsa to confront Arenado face-to-face, and he told him that he wasn't going to even get a September callup. Even the next spring, when Arenado put on an impressive display, O'Dowd didn't back down.
By the end of April 2013, however, Arenado had met expectations and got the call to the big leagues.
This is just another challenge for Arenado to meet. He's not the first player -- young or old -- to let emotions get the best of him.
And sometimes the appearance is actually worse than the emotion.
Tulowitzki knows that well.
In a 2008 season that saw him sidelined early with a torn quadriceps tendon, he had been back in the lineup for only 12 games before he suffered a lacerated right hand on July 4 from the splinters of a bat he slammed to the ground after flying out with two on to end the sixth inning of a game the Marlins led, 13-12. He spent the next 15 days on the disabled list.
"I've snapped worse than that 20 times," said Tulowitzki, "but I had a broken bat, and when I threw it into the bat box, it sliced my hand. It's a mistake I'll never make again."
And the Rockies are hoping that Arenado's slow gait to first is something they won't see again either.