Drew Brees, the New Orleans quarterback, had posted on Twitter earlier in the week that his team would kneel together before the anthem and then stand during it to show 'solidarity for all'.
In a gesture initiated last season by then-San Francisco 49ers quarterback Colin Kaepernick, several NFL players have routinely knelt on one knee during the playing of the American anthem.
It is intended to call attention to what the protesting players see as a pattern of racism in the treatment of African-Americans by US police.
The three Dolphins players who knelt had also been part of the protest movement last year.
London-born Jay Ajayi, who plays for the Dolphins and poster boy of the International Series, stood during the US national anthem.
Last week, Ajayi was one of 10 Miami Dolphins players to wear an #IMWITHKAP T-shirt in warm ups and one of seven to stand during the playing of the Star-Spangled Banner before defeat by the New York Jets.
But while wide receiver Kenny Stills again wore a garment in support of out-of-work former San Francisco 49ers Colin Kaepernick, Ajayi was decked in a hoodie before the game with New Orleans Saints.
Offensive tackle Laremy Tunsil stood behind the trio and stretched. The Saints were true to the pre-match declaration of quarterback Drew Brees, who said the Saints would kneel before and stand during the anthem.
Ajayi, who was born in London and moved to Texas aged seven, missed the Dolphins last game in Wembley two years ago due to a cracked rib.
But he suited up and made his Wembley debut despite being questionable with a knee injury.
Arsenal fan Ajayi embraced hero Thierry Henry prior to kick-off, and the Frenchman was promptly grabbed by fellow Gunners fan Ndamukong Suh, the giant defensive tackle.