Russell Wilson threw three second-half touchdown passes as the Seattle Seahawks overcame the Giants 24-7 in New York.
Wilson hit Doug Baldwin with a go-ahead 22-yard touchdown pass midway through the third quarter, connected with Richardson from 38 yards out early in the fourth, before closing out the scoring with a one-yard toss to Jimmy Graham with just over two minutes to go.
The Seahawks were equally impressive on defence, limiting the Giants' receiver-depleted offense to only 177 yards, 14 first downs and forcing an Eli Manning fumble that led to the Richardson TD.
The Giants, who stunned Denver on Sunday night for their first win of the season, were only in the game for as long as they were because of their defensive effort - they limited Seattle to just a field goal in the first half.
The unit also set-up New York's only score with a forced fumble and a 32-yard return by Landon Collins to the Seahawks 17-yard line. It led to a five-yard TD toss to tight end Evan Engram.
Blair Walsh kicked a 39-yard field goal late in the first half then, after Seattle took the lead with Baldwin's TD, the Giants had a chance to tie the game early in the fourth quarter but a 47-yard field goal by Aldrick Rosas was wide right.
Richardson's touchdown was a contested catch by Collins that was eventually awarded to the offense after review, while Graham, who had dropped a touchdown pass on the first play of the second quarter, caught one late on.
Elsewhere, in the other late games in the NFL....
Cowboys 40-10 49ers
Ezekiel Elliott ran for 147 yards and two touchdowns, and caught a 72-yd touchdown pass, leading Dallas (3-3) over winless San Francisco (0-7).
Quarterback Dak Prescott also completed 16 of 25 passes for 234 yards and three touchdowns, as well as running in for one, as the Cowboys ended a two-game losing streak.
Bengals 14-29 Steelers
Le'Veon Bell carried 35 times for 134 yards against the NFL's second-ranked defence to guide Pittsburgh (5-2) to victory over Cincinnati (2-4).
Broncos 0-21 Chargers
Los Angeles (3-4) blanked Denver (3-3) to win their third straight game, while their opponents have now lost three of their last four.