MINNEAPOLIS — Rob Ryan bragged shortly after the Dallas Cowboys hired him in January that the team would sport “a great defense” with him as its coordinator. So far, it seems like an empty boast. The Cowboys eked out a 23-17 win in Saturday night’s dress rehearsal for the regular season, but they allowed Adrian Peterson (81 yards on 14 carries) and Donovan McNabb (49-yard touchdown pass) to show them up. In the first game at the Metrodome since the building’s roof collapsed in a snowstorm Dec. 12, the Cowboys’ second-team defense also struggled. Joe Webb completed a 43-yard pass before he scored on a 10-yard run to pull the Vikings within 20-17 in the third quarter. “We played with some passion, some emotion, some enthusiasm,” Dallas coach Jason Garrett said. “But we have to clean up a lot of things.” It should start with the defense, but time is running out. Thursday’s preseason finale at Miami will probably be devoted to younger players, and there are only a handful of practices left before the Sept. 11 opener at the New York Jets. “We’ll fix it even if we have to stay after practice and work extra,” Pro Bowl nose tackle Jay Ratliff said. “Whatever it takes, we are going to get it done.” While Ratliff’s comments reflected a sense of urgency, owner Jerry Jones preached patience. “The developing of what we are going to do on our defense is of no more concern to me than the developing of the team,” Jones said. The Vikings ripped through the defense on their first possession, needing just seven plays to cover 83 yards. After Peterson gained 4, 6, 2 and 6 yards on his first four carries, McNabb tossed a 49-yard play-action pass to Bernard Berrian for a 7-0 lead. Safety Abram Elam was in position to make a play on the ball, but it went through his hands. Peterson finished the first half with 69 yards on 11 carries. Dallas (2-1) also struggled to stop the run in the preseason opener against Denver, but Jones said he’s not worried. “At this time, no I’m not,” Jones said. “I’m very calm. I know what they are trying to do.” Dallas led 17-10 at halftime even though Minnesota held a commanding 216-157 edge in total yards. Gerald Sensabaugh was the difference. The veteran safety justified Dallas re-signing him in free agency by blocking a 47-yard field-goal attempt that Alan Ball returned 20 yards for a TD and intercepting a tipped McNabb pass that set up a 77-yard drive that Felix Jones capped with a 5-yard scoring run. The block was negated later in the second quarter when the Vikings’ Cord Parks returned a kickoff 53 yards to the Cowboys’ 42. Seven plays later, Ryan Longwell kicked a 44-yard field goal. Offensively, Dallas had several bright spots, starting with a turnover-free performance by Tony Romo, who was 15 of 20 for 141 yards without a TD. Romo guided the Cowboys to a TD and a field goal. His favorite target was Dez Bryant, who caught five passes for 67 yards, including three for 41 on the drive that resulted in Felix Jones’ TD run. Another bright spot: rookie running back DeMarco Murray carried seven times for 32 yards in his preseason debut after missing camp with a hamstring injury. Among the players suffering injuries was tight end Martellus Bennett, who was carted off the field in the third quarter with what Jerry Jones said was a high ankle sprain. Ball suffered a left elbow injury in the first half and did not return. Undrafted rookie Dan Bailey kicked field goals from 37, 38 and 41 yards, a performance that could give him the edge in his competition with David Buehler, who missed his second straight game with a hip injury.