That competition was quickly interrupted, however, as Jackson suffered a Grade 1 sprain of the medial collateral ligament in his left knee on the second day of practice.
The injury wasn't serious — Jackson isn't expected to miss much time and coach Brad Childress said he wasn't concerned — but it does give Rosenfels a potential leg up in the competition.
Rosenfels has had a roller-coaster ride since being obtained by the Vikings from Houston for a fourth-round pick near the end of February. At that point, Rosenfels thought he was going to get the first real chance of his nine-year NFL career to win a starting job.
That changed in late April when the New York Jets released Favre from their reserve/retired list and speculation turned into confirmation that the Vikings were extremely interested.
Now, the 31-year-old Rosenfels finds himself poised to get the opportunity he has long desired.
"For J.D. (third-string quarterback John David Booty) and I, it always helps to get more reps," Rosenfels said. "You can't really have too many reps. I'm just trying to take advantage of every rep I get."
Rosenfels admitted on the first day of camp that sharing the snaps with the first team wasn't ideal. That's especially true because he isn't completely familiar with many of his teammates.
"It's not the premier situation you'd like to have," Rosenfels said. "You'd like to be throwing with Bobby (Wade) and Bernard (Berrian) and (Visanthe Shiancoe) and all those guys. Every throw."
Rosenfels has started 12 of the 32 games in which he has played in the NFL, including five each of the past two seasons with the Texans. Houston runs a West Coast system that has some similarities to the Vikings' offense but they are not identical.
Rosenfels, in fact, is having to make more adjustments than he expected when he arrived in Minnesota.
"A lot of the language is similar," he said. "It would be like two people reading books. If it's in English, it's much easier to read and make sense out of it all. But there are a lot of differences, in my opinion, between this offense and the Houston offense."
The fact Rosenfels still needs to find a comfort zone was pretty obvious in the early practices as it appeared he was thinking about executing the plays more than Jackson. Jackson is entering his fourth season with the Vikings and has started 19 games in that time.
"At this time Tarvaris has a little bit more knowledge of our system," Vikings offensive coordinator Darrell Bevell said. "He is an athletic quarterback. He's got a very strong arm and those would be the positives about him. Sage still has got good feet but probably doesn't run as well as Tarvaris.
"Their arm strengths are different but there are still things that both of them do well. Sage has been in this system before, just not ours. Verbiage is different for him but he's still got to pick that up."
While Rosenfels will have to answer plenty of questions about his progress, one topic he is hoping to avoid is anything related to Favre.
"I don't think about it," Rosenfels said. "I wasn't thinking about it out (on the field) at practice, and I'm not thinking about it right now until you just asked me that question. The more you guys stop asking those questions the less I'll have to even worry about it."
CAMP CALENDAR: The Vikings will have a second night practice from 7 to 9:10 p.m. on Aug. 7. The team will break camp after two practices on Aug. 12.
"We never make any pre-conditions on how the season should turn out or what conditions would be necessary," Wilf said. "We're very happy with our coach and the coaching staff and the players. We're very excited for this year."
Peterson rushed for 1,760 yards last season and now has his sights set on the 2,000-yard mark. "It's something I think about and dream about, but I don't focus on it because you'll never accomplish it that way," he said. "That's my bar. It will always be 2,000 or more. God willing and with the guys I have surrounding me, I'll be able to accomplish that one day."
QUOTE TO NOTE: "The hoopla is over and we have a phenomenal team and we have high expectations and we have a lot of work to do to meet those expectations, so let's get to business." — Defensive end Jared Allen talking about the Vikings' pursuit of Brett Favre having ended and how the team must now get to work.