The wildcard – now ranked 121 in the world – started strongly despite the Frenchwoman’s superior ranking and opened up a 3-1 lead in what was a nervy first set.
However, Watson was unable to maintain the high tempo and surrendered the subsequent three games as Razzano led for the first time in the match.
The Brit managed to break her opponent to level the opening stanza up at 4-4, but yet again failed to hold serve in what proved to be a decisive ninth game. The world number 81 then went on to serve out the set in 43 minutes.
With momentum in her favour, Razzano capitalised on Watson’s error-strewn game, punishing every poor shot to seal the match with a bagel.
Earlier, for former world number three Nadia Petrova, now languishing at number 205 in the rankings, there were flashes of the form that carried her to 13 career titles as the Russian saw off Poland's Urszula Radwanska 7-5 1-6 6-4.
"For some people they might think it's hard especially being where I am right now," the 31-year-old Petrova told Reuters.
"At this stage of my career it is kind of difficult but on the other hand with all the experience I have and the knowledge knowing when are the important moments, when to step in and take the initiative it can be easier."
The perks afforded to the world's top-ranked players, for the moment at least, no longer available to Petrova.
"It's humbling," admitted Petrova. "When you arrive at a tournament (as top-ranked player) you know you have all the luxuries.
"You can have a box of balls, you can get a rental car, you can get an extra hotel, you can get a suite and right now those things do not exist for me anymore.
"You have to start from the beginning."
For Petrova, it is almost like starting over again as she must play qualifiers to get into tournaments or depend on the charity of a wildcard berth.
With 13 singles and 24 doubles titles, Petrova is just one of three active players, along with Serena Williams and Venus Williams, with 10-plus victories in both events.
She had been a fixture in the top 15 for almost a decade and ended the 2012 season as the world number 12.
But a hip injury in 2013 followed by the death of her mother in December forced Petrova off the WTA Tour and sent her ranking on a nosedive.
"I'm just taking it match by match and at the moment I do lack little bit of match play, it's been a long time since I've been on a roll so it is frustrating and challenging," said Petrova. "Obviously going back into (qualifiers) is not an exciting thing for me to do, especially since it has been over 10 years since I have been part qualifying.
"Other than that I am just focused on the game and things I need to do on the court."
Sony Open results
Madison Keys (U.S.) beat Anett Kontaveit (Estonia) 6-3 6-2
Alison Riske (U.S.) beat Nadiya Kichenok (Ukraine) 1-6 7-5 6-2
Zarina Diyas (Kazakhstan) beat Alexandra Cadantu (Romania) 6-4 3-6 6-2
Andrea Petkovic (Germany) beat Maria Teresa Torro (Spain) 6-3 6-4
Yvonne Meusburger (Austria) beat Lourdes Dominguez Lino (Spain) 6-3 6-0
Ajla Tomljanovic (Croatia) beat Kristina Mladenovic (France) 7-6(4) 6-4
Barbora Zahlavova Strycova (Czech Republic) beat Monica Niculescu (Romania) 6-3 6-4
Christina Mchale (U.S.) beat Zheng Jie (China) 6-4 6-2
Nadia Petrova (Russia) beat Urszula Radwanska (Poland) 7-5 1-6 6-4
Coco Vandeweghe (U.S.) beat Marina Erakovic (New Zealand) 6-4 7-6(6)
Donna Vekic (Croatia) beat Kimiko Date-Krumm (Japan) 7-6(2) 6-2
Olga Govortsova (Belarus) beat Shahar Peer (Israel) 2-6 6-0 6-3
Kiki Bertens (Netherlands) beat Victoria Duval (U.S.) 7-6(5) 6-1
Paula Ormaechea (Argentina) beat Katarzyna Piter (Poland) 7-6(0) 6-1
Patricia Mayr-Achleitner (Austria) beat Karin Knapp (Italy) 3-6 6-1 6-4
Lauren Davis (U.S.) beat Zhang Shuai (China) 6-2 6-3
Rebecca Peterson (Sweden) beat Mona Barthel (Germany) 6-4 4-2 (Barthel retired)
Peng Shuai (China) beat Karolina Pliskova (Czech Republic) 7-5 6-0
Vania King (U.S.) beat Estrella Cabeza Candela (Spain) 6-0 6-0
- Sports & Recreation
- Nadia Petrova