The Frenchman struck three minutes into the second half but Chelsea had some nervous moments in the closing stages as Porto pushed hard for an equaliser before having Fernando sent off in injury time for a second caution.
With Atletico Madrid being held to a goalless home draw by APOEL Nicosia in the other Group D game, Chelsea manager Carlo Ancelotti was more than content.
"We couldn't hold on to the ball in the second half and could not control the game but Porto are a good side," the Italian told reporters.
"You can't always play your best and sometimes you have to win when you are below your best, that's an important characteristic for a team."
The last time Chelsea were in European action here, their hearts were broken by Barcelona's last-gasp equaliser in the second leg of last season's semi-final.
Didier Drogba and Jose Bosingwa were suspended on Tuesday following their rants about the referee in that encounter.
The hosts seemed to miss Drogba in the first half as strike duo Anelka and Salomon Kalou flitted in and around the box without really establishing a presence as neat midfield passing failed to develop into many attacking openings.
TORRENTIAL RAIN
Porto looked dangerous as they broke quickly and kept John Terry and his defence on their toes in conditions made awkward by torrential rain.
Fredy Guarin headed over the bar and, in injury time, Raul Meireles popped a tame header straight at keeper Petr Cech when presented with the best chance of the first half.
Things changed within three minutes of the restart as a Kalou flick sent Anelka through on goal. His initial shot was parried by Helton but the Frenchman reacted smartly to force in the rebound from a tight angle.
The diving Helton did well to save a Kalou header after an hour while Branislav Ivanovic thundered another header inches over from the resulting corner.
Chelsea could not find the second goal and memories of Andres Iniesta's injury-time strike for Barcelona began to emerge as some sloppy play offered the visitors too many sights of goal.
The defence, though, stood firm to set the Londoners off on a journey they hope will end at the final in Madrid in May.
Having reached the semi-finals five times in the last six campaigns, Ancelotti's target is to make this the season Chelsea finally get over the line.
Porto coach Jesualdo Ferreira was not writing off his team's chances of progressing either.
"I think we should look at that game in a positive way," he said. "In the second half we controlled the game for long periods, we had a lot of shots and I think we were unlucky not to score.
"It's just the first game and we are still in a good position in the group. The door is still open."
