Bill Kostroun / Associated Press

Chase Blackburn (57) and Michael Johnson (20) led a stout Giants defense.

It was over when ...
Giants DE Justin Tuck sacked 49ers QB J.T. O'Sullivan and forced him to fumble late in the fourth quarter. The ball ultimately was kicked out of the end zone by San Francisco rookie WR Josh Morgan for a safety and the 49ers' hopes of a comeback were dashed with five minutes to go.

Game ball
Filling in for an injured Antonio Pierce, backup LB Chase Blackburn stepped in and had a career game. The fourth-year player was all over the field and finished with 10 tackles, a sack and a forced fumble as he made life miserable for 49ers RB Frank Gore and O'Sullivan.

Key stat
San Francisco's rushing attack was unable to give O'Sullivan any help as it averaged only 2.2 yards per carry on 16 attempts. That meager output ended up being too much for the passing game to overcome.

Noteworthy
O'Sullivan had four fumbles, giving him a league-high nine on the season. ... Morgan had his first career touchdown catch. ... The 49ers returned a blocked field goal for a touchdown for the second straight week. ... Giants safety Michael Johnson had his first career interception in the second quarter and added his second pick minutes later. ... Tom Coughlin improved to 4-0 against the 49ers.