In the 2005 draft, the Vikings used two of the first 18 picks to select Troy Williamson and Erasmus James. The first couldn't play in the NFL. The second didn't seem to want to.

Since then, the Vikings have used seven first-round picks to acquire players. "Other than me, I don't think they've missed too many,'' Chad Greenway said.

Greenway, the Vikings' star linebacker, needn't be self-deprecating. While the rest of the NFL tries to figure out how the Vikings became the most surprising success story in the league, the simplest explanation is the most accurate: They have amassed quite a few good players.

And they have good players because they have turned their first-round draft picks into winning lottery tickets.

Only three teams in the NFL have a better record than the Vikings. With a home game against 2-4 Tampa Bay at the Metrodome on Thursday night, under circumstances that have proved difficult for road teams, the Vikings have a chance to improve to 6-2 halfway through what most rational people assumed would be a season of gradual progress after last year's 3-13 debacle.

Suddenly the roster doesn't look so anemic, thanks to a series of successes at the top of the draft.

In 2008, the Vikings traded their first-round pick, with other assets, to Kansas City for Jared Allen. If you include Allen among the Vikings' recent haul of first-rounders, here's the talent infusion that has made their improvement possible:

• 2006: Greenway with the 17th pick.

• 2007: Adrian Peterson with the seventh pick.

• 2008: Allen for the 15th pick.

• 2009: Percy Harvin with the 22nd pick.

• 2010: Vikings trade out of the first round, then take cornerback Chris Cook early in the second round.

• 2011: Christian Ponder with the 12th pick.

• 2012: Matt Kalil and Harrison Smith with the fourth and 29th picks.

While using only one draft pick higher than the 12th selection, the Vikings erected the scaffolding of a deep, talented, roster.

Peterson, Allen and Harvin rank among the best players in the league. Greenway has become one of the most important players on the team. Ponder, despite his current slump, remains a promising quarterback who fits the Vikings' plans. Cook is a prototypical physical cornerback. Kalil and Smith immediately upgraded two weak spots on the roster, offensive line and the secondary.

''Rick [Spielman, Vikings general manager] and the organization have done a great job of bringing in players who are good guys, first and foremost, but who also fit into what we're trying to do schematically, which is great,'' Greenway said. ''They're putting guys in position to be successful right away, and getting their careers off to a good start. And they're buying in and believing in their draft choices and sticking with them.''

Despite all of the talk of their Code of Conduct and avoiding problematic players in the wake of the ''Love Boat'' scandal, the Vikings have embraced risk. At the time they were acquired, Peterson was considered an injury risk; Harvin, Allen and Cook carried personal baggage.

Vikings coach Leslie Frazier said that several times he has recommended against acquiring players of dubious character. He and Spielman haven't let flawed résumés steer them away from superior athletes.

''I was heavily involved with Jared's decision,'' Frazier said. ''I was involved with Percy's decision, because we had faced a similar decision the year before on a receiver that we had passed on. Adrian wasn't a tough decision -- we didn't expect him to be there, and when Adrian Peterson drops in your lap, you take him.

''With Jared, I believed he wanted to change as a person. That let me know that he would fit with us. I need to get a feel for the person and what's important to them, and then I can sign off and say, 'Yeah, Rick, I think this guy is a good idea. Fortunately, Rick listens and we can work together on some of these decisions.

''It's been good. Jared is a perfect example.''

Jim Souhan can be heard Sundays from 10 a.m. to noon and weekdays at 2 p.m. on 1500-AM. His Twitter name is SouhanStrib. •