The men's victory makes it a double double win for New Zealand at the Dubai Sevens after the national women's side took out their tournament the day before.
The first try of the men's final went to New Zealand with Ng Shiu powering through USA the tackles to get the first points on the board, successfully coverted by the accurate Andrew Knewstubb. They had the halftime lead of 7-0.
Down to six players due to a yellow card for against Luke Masirewa for a high tackle in the second half, USA took the opportunity to get their first points on the board with Stephen Tomasin scoring their first and only try of the game. The score sat at 7-5 with just four minutes to go.
However, a knock-on by USA allowed New Zealand to take control wih Collier out-pacing his opposition to score another try for New Zealand.
Down 14-5, USA were seen to have eight players on the field, giving a penalty to New Zealand at halfway and allowing another opportunity for New Zealand.
That opportunity was taken by McGarvey-Black who secured the final try of the match and sealed the 21-5 win for New Zealand - their first tournament win in Dubai since 1999.
The All Blacks Sevens' successful start to their world sevens series adds to the already successful 2018 coming away as Commonwealth Games gold medallists and the Rugby World Cup Sevens title.
The HSBC Player of the Final went to Knewstubb, who was also named the Player of the Tournament.
Finals day for the All Blacks Sevens started well, with the squad only allowing Scotland to score once in the final minutes of their Cup quarterfinal that ended with a 21-7 victory for the Kiwis. It was followed by New Zealand's undoubtedly tough semifinal against England with the local side giving everything in defence.
On day one, the All Blacks Sevens were undefeated in their three pool play matches, beating Wales 28-7, Spain 28-17 and USA 24-7 and took the top spot in Pool C.
The New Zealand men's sevens side now have six days before their second tournament of the world series in Cape Town on December 8-9. The World Rugby Sevens Series is a qualification pathway to the 2020 Olympic Games in Tokyo and to confirm a place teams have to finish in the top four.
