The Buffalo Bills didn’t wait until the second half to fall behind this week.

Buffalo (2-3) never had a chance during a 45-3 drubbing by the San Francisco 49ers (4-1) at Candlestick Park on Sunday.

Niners quarterback Alex Smith looked like the first overall pick he once was by converting on 18 of 24 passes for 303 yards and three touchdowns.

His main target was another top 10-draft pick in Michael Crabtree, who brought in six catches for 113 yards and a score.

On the ground, Frank Gore’s 14 carries for 106 yards and a TD led the way for a San Francisco team that outgained Buffalo 622-215 in total yards.

A big part of that was Ryan Fitzpatrick throwing for only 126 yards on 14of 26 passing with one interception.

In the rushing department, the Bills, led by Fred Jackson and C.J. Spiller, produced only 84 yards, and 35 of those came on a scamper by utility offensive player Brad Smith.

Buffalo was hanging in the game, down 10-3 until late in the second quarter.

After forcing a Colin Kaepernick fumble and recovering in the opening half’s final minute, Bills tight end Scott Chandler was stripped by linebacker Patrick Willis leading to a 28 yard Crabtree touchdown catch.

That score made it 17-3 entering halftime and the 49ers would not look back from there scoring 28 second half points a week after Buffalo allowed 45 in the final 30 minutes against New England.

The Bills continue their western road trip in Week 6 when they take on the Arizona Cardinals (4-1) at University of Phoenix Stadium at 4:05 p.m. ET.