Fidow collapsed a maul for his first yellow card, and slid in knees first to stop Sean Maitland scoring for his second sin-bin offence with five minutes to go.
The two yellows added up to a red to keep Samoa’s terrible disciplinary record going at the World Cup.
They had two yellows in their first game, and Fidow was also warned after that game for punching, although he didn’t get punished during it.
Scotland’s chances of making the quarterfinals would have been left hanging by a thread if it had slipped to a second straight loss in Pool A.
It’s still by no means certain but it’s better than where it was after a 27-3 walloping by Ireland to open the World Cup.
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First-half tries by wing Maitland and scrumhalf Greig Laidlaw, and a dropped goal from distance by fullback Stuart Hogg put Scotland out of sight of Samoa at Kobe Misaki Stadium. Hogg launched his drop from near halfway and wide out on the left wing for a 20-0 halftime lead.
Scotland’s two penalty tries came in the second half as it bounced back resoundingly from the Ireland walloping.
Both teams dropped the ball constantly in the first half hour on a sweaty night at Kobe Misaki Stadium, where the closed roof exacerbated the humid, slippery conditions.
But Maitland did catch a cross-kick from flyhalf Finn Russell on the left to get the Scots going and they kept their winning run up against Samoa at the Rugby World Cup.
The Scots have won all four meetings now.
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The Samoans, who lost two players to bans for dangerous tackles after those yellow cards against Russia, lost in two tries against Scotland to poor tackles, and the other two to poor discipline.
After catching Russell’s pinpoint cross-kick, Maitland slipped out of a Belgium Tuatagaloa effort to scamper over the line in the 30th minute.
Russell set up the second, too, breaking the first line of defence and finding flanker Jamie Ritchie in support.
Ritchie fed Laidlaw, who bounced out of Tim Nanai-Williams’ attempted tackle and scampered away.
Hogg landed the dropped goal from around 50 meters out — amazingly Scotland’s first in a Test for more than five years.
Samoa was given its first double-whammy in the 57th when Scotland earned a penalty try and Fidow his first yellow for collapsing a maul that was heading for the tryline.
The bonus-point fourth try appeared to be eluding Scotland until Maitland made a late break down the left.
Fidow’s cross-covering was good, but his tackle technique wasn’t.
As Maitland slid for the line, Fidow went in knees first, hitting Maitland hard enough to loosen his grip on the ball.
There were two field invaders in the second half in Kobe.
The first fan ran across the field shirtless and the second in his underwear as the nighttime temperatures hovered near 30 degrees Celsius.
SCOTLAND 34 (Sean Maitland, Greig Laidlaw tries; 2 penalty tries; Laidlaw 2 conversions, penalty, Stuart Hogg dropped goal) SAMOA 0. HT: 20-0
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