Brock Purdy threw three touchdown passes, two to George Kittle, and the San Francisco 49ers — after building a 20-point lead — held on to defeat the host Seattle Seahawks 36-24 on Thursday.

Purdy also threw a 76-yard scoring strike to Deebo Samuel Sr. as the 49ers (3-3) moved into a first-place tie with the Seahawks (3-3) in the NFC West.

Geno Smith threw a 9-yard touchdown pass to Tyler Lockett with 1:44 remaining to pull Seattle within 29-24.

San Francisco’s Kyle Juszczyk scored on a 6-yard run with 1:17 left to clinch the victory. That came two plays after rookie Isaac Guerendo broke free on a 76-yard run. Guerendo rushed for 99 yards on 10 attempts after Jordan Mason, who entered the game second in the NFL in rushing, left with an apparent left shoulder injury.

Mason gained 73 yards on nine carries. Purdy was 18 of 28 for 255 yards, and Samuel produced 102 yards on three receptions. Kittle had five catches for 58 yards.

The 49ers forced three turnovers and turned them into 12 points.

Smith connected on 30 of 52 passes for 312 yards with one touchdown and two interceptions. The Seahawks tried to establish the running game but gained just 52 yards on 20 carries.

Laviska Shenault Jr. scored on a 97-yard kickoff return for Seattle, which took its third consecutive loss.

Purdy’s 10-yard touchdown pass to Kittle with 10:07 left in the third quarter gave the 49ers a 23-3 lead.

The 49ers, who blew double-digit leads in divisional losses to the Los Angeles Rams and Arizona Cardinals earlier this season, then saw Shenault return the ensuing kickoff to spark a Seattle comeback.

Kenneth Walker III scored on a 1-yard run with 1:24 left in the third to pull the Seahawks within 23-17.

Niners rookie Renardo Green stepped in front of DK Metcalf and picked off a Smith pass to set up Kittle’s second touchdown, a 9-yard reception with 6:20 remaining in the game, to make it 29-17.

The 49ers took a 16-3 halftime lead. San Francisco had a 244-133 edge in total offense, including 105-24 on the ground, and forced a pair of turnovers — an interception of a Smith pass near the goal line and a Shenault fumble on a kickoff return.

The lone touchdown of the half was the 76-yarder to Samuel down the left sideline with 13:30 remaining in the second quarter.

San Francisco kicker Matthew Wright, signed earlier in the week after Jake Moody sustained a high ankle sprain Sunday, converted all three of his field-goal attempts in the first half, from 25, 41 and 35 yards.