Then he looked up to determine just how much his efforts helped shifty tailback Jahvid Best.
"He's 60 yards downfield," Mack said. "I thought, 'I could have given up a good five seconds ago.'"
It probably won't be the last time the sophomore scampers away. Best averaged 155.5 yards rushing to help the Golden Bears (2-0) rise to No. 23 in the country entering Saturday's game at Maryland (1-1).
There are even early whispers of a Heisman candidacy thanks to a 200-yard outburst in last week's 66-3 rout of Washington State.
Before Best, California never had a player with two rushes of 80 yards in a career. He did it in a single game, rumbling 80 yards on the game's first play and 86 yards early in the second half against the Cougars to earn the attention of a Maryland defense known in recent years for its struggles against small, elusive backs.
"He's electric," Maryland safety Antwine Perez said. "He's a pretty exciting football player. You know he can run."
That much was obvious well before he arrived at Cal. Much like Maryland tailback Da'Rel Scott, Best was a decorated high school sprinter. Steered into track by his mother, Best won the California state title in the 100-meter dash in 10.31 seconds as a senior.
Speed is the most obvious trait that has helped Scott, who ranks fourth in the nation at 160 yards a game, and Best thrive in their first seasons as starters.
Yet it might not be the only skill extracted from the experience.
"I think composure," Best said. "When you go to big track meets, there's a ton of people looking right at you. It's kind of the same feeling when you have the ball in your hands. Learning to deal with that pressure, it helps here because I can block out the crowd and focus on the field."
His track ability was put to use for spurts last season, when he backed up Justin Forsett and also returned kicks. A hip injury cost him the final three games, but coach Jeff Tedford realized Best's value to his team this season.
He isn't like Marshawn Lynch, who passed through Tedford's program earlier this decade and developed a reputation for bowling defenders over. But he might prove to be equally effective, especially because of Cal's eagerness to use him in the passing game.
"He's not just a running back," said Maryland coach Ralph Friedgen, who compared Best to former Southern California tailback Reggie Bush. "He can be a wide receiver. They're going to move him around and try to get him matched up the best way they possibly can."
The Bears already have. Best shared the team lead in receptions as California started to shake off last season's disappointing 7-6 season with an opening-week victory over Michigan State.
It earned him a start against Washington State, which led to a performance that drew praise from analysts across the country. Just not from Best himself.
"I think there's a lot left to get better at," Best said. "There were a couple bad reads and a couple bad runs. It's kind of like I'm blessed; I'm still doing pretty good, but there's still a lot to get better at."
That can't be a pleasant prospect for Maryland this week or the rest of the Pac-10 in the next few seasons. Mack believes the 5-foot-10, 193-pounder already has Forsett's ability to hit holes quickly.
Toss in the speed and the separation it can create and the nascent Heisman hype Best admits he hears but doesn't pay much attention to could blossom quickly.
"He makes it look simple," Mack said. "He was just out there running around, and he got the ball, he hit the hole and then he took it. He's just a really good runner. It didn't look difficult."
With that sort of speed, it's not difficult to believe, either.