England will take on France and Spain will face Austria on Sunday, while hosts the Netherlands will play against Sweden and holders Germany tackle Denmark a day earlier.
Portugal were pushing for a goal that would have seen them through, but Mendes narrowly missed Silva's cross in front of the goal in the first half, and England then held on to their lead comfortably.
In a rare chance, Laura Luis sent her volley into keeper Siobhan Chamberlain in stoppage time.
"We've gone and won a group with three wins against three difficult teams," said England coach Mark Sampson.
"We've scored ten and conceded one â- nobody is anywhere near us, not even scored half of the goals that we got."
"We're in a position where we wanted to be, we have momentum, confidence behind us. We're in form."
Portugal coach Francisco Neto said his girls had left everything on the pitch in the last game of their first Euro.
"I'm not happy with the result, but I'm very happy with the girls. England are one of the best teams in the world, but Portugal tonight, I think, deserved at least a draw."
Spain dominated possession against Scotland, and they could have taken the lead, but Scotland keeper Gemma Fay narrowly palmed out Marta Torrejon's free-kick on five minutes.
Half an hour later, Fay dived superbly to save Jennifer Hermoso's header before clearing Irene Paredes's header onto the post in the same minute.
Before half-time, Fay ran out and handled the ball outside the box, but Torrejon missed from the ensuing free-kick.
A second goal would have been enough for Scotland, but Leanne Crichton blasted her shot from seven metres over the bar and substitute Lana Clelland also sent a left-footer over.
At the other end, Silvia Meseguer rattled the crossbar with a long-range effort and Scotland's Ifeoma Dieke cleared the ball off the goal line after another superb save by Fay.
"I'm very, very proud. We couldn't have done more today," said Scotland coach Anna Signeul, who is leaving after 12 years at the helm to take over Finland
"Tonight was fantastic. They showed what we are all about."
Spanish coach Jorge Vilda said his team was "perhaps a little too nervous."
"In the second half we definitely improved our positioning and had great possession but we didnât take our chances as well as I wanted.
Source: AFP
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