Saints QB Drew Brees couldn't bring his team back from too many mistakes, including a game-changing interception with 22 seconds left in the first half that the 49ers returned for a touchdown on Sunday. (US Presswire)

The Saints were doing everything they needed to beat San Francisco before Drew Brees threw a game-changing interception the 49ers returned for a touchdown with 22 seconds left in the first half.

Suddenly, what they hoped would be a 17-7 lead at the break turned into 14-14, and when Brees threw a second pick-six early in the third quarter, the Saints had virtually no chance. San Francisco is far too good a team to lose when it scores two defensive touchdowns, and the 49ers held on to win 31-21.

Offense: D

Against almost anyone else, a game where the offense scored only more touchdown than the opposing defense would merit an F, but San Francisco has the best defense in the NFL. Brees led two impressive TD drives –a 10-play, 79-yarder in the first quarter and an eight-play, 80-yarder in the third quarter--while completing 26 of 41 for 267 yards and three scores.

His 10-yard TD pass to Marques Colston that put the Saints ahead 14-7 was a perfect throw to the back of the end zone. But his mistake right before halftime killed the Saints -- tight end Jimmy Graham was not open and Brees threw it right to LB Ahmad Brooks. The second pick-six came, when he threw too high for Colston in the middle of the field, was more excusable. He was trying to make a play and was slightly off. Once San Francisco got ahead, the New Orleans offense had no shot. The 49ers had no sacks in the first half and five in the second. The Saints managed just 59 yards on 21 carries, no surprise against the 49ers outstanding run defenders. Previous game’s grade: B+

Defense: C

For the most part, the defense played OK, holding the 49ers to 17 offensive points with the help of a missed field goal and a blocked field goal. San Francisco is the first New Orleans opponent to gain fewer than 400 yards, finishing with 375. Still, the Saints allowed three big drives. A mix-up left Mario Manningham wide open for a 40-yard gain with CB Jabari Greer trailing him as the 49ers cruised 80 yards in four plays for their first TD. A run blitz on third-and-2 left LB Curtis Lofton in a mismatch with TE Delanie Walker, leading to a 46-yard gain on a six-play, 80-yard TD drive to start the second half. And San Francisco converted three third downs, including a third-and-11, on an 85-yard drive that consumed 9:26 before its clinching field goal. The run defense was better than the numbers (31 carries, 144 yards) suggested --Frank Gore’s longest run in 19 attempts was 14 yards -- but the Saints missed too many tackles on the 49ers receivers and elusive QB Colin Kaepernick, who was not sacked despite being pressured at times. Previous game’s grade: A-

Special Teams: A-

The Saints won the special teams battle. Thomas Morstead had a net of 47.8 yards on five punts and placed two inside the 20. Gunner Rafael Bush made a flying recovery of a muffed punt at the 11, leading to the Saints’ second TD. Malcolm Jenkins blocked a field goal in the final minute that could have resulted in a New Orleans touchdown if the deflected ball had taken a better bounce. Travaris Cadet averaged 29.6 yards on five kickoff returns, getting the ball past the 20 every time. Previous game’s grade: A-

Coaching: B

Down to their third-string right tackle, the Saints were in a precarious situation entering the game against San Francisco’s dominant D-line. After worrying too much about the 49ers’ pass rush on their first two possessions with quick passes, offensive coordinator Pete Carmichael started running his normal offense, with extra help on the right side. The decision worked, but when the Saints had to go to a fourth right tackle after Bryce Harris’ leg injury, Carmichael was in an impossible situation. The 49ers’ five sacks in the second half were inevitable. The defense appears much more comfortable in Steve Spagnuolo’s scheme but simply got beaten on a few plays. This loss was not on the coaches. No one beats San Francisco while giving up two interceptions returns for TDs. No one. Previous game’s grade: A

Follow Saints reporter Guerry Smith on Twitter @CBSSaints.