Benfica took the lead deep into first half stoppage time when Gianluca Prestianni was clumsily felled in the area by Haris Zeb.
Di Maria, who converted a spot kick in the opening 2-2 draw against Boca Juniors, sent Garrow the wrong way.
At halftime, the match became the fourth in the last four days at the tournament to be impacted by a suspension for adverse conditions, with a storm arriving at the Inter&CO Stadium.
When play eventually resumed, Benfica came back out strongly.
Vangelis Pavlidis bundled his way through and smashed home to double Bruno Lage’s team’s lead in the 53rd minute, with Renato Sanches netting the third 10 minutes later from outside the box with a deflected effort.
Luxembourg midfielder Leandro Barreiro bagged a brace to expand Benfica’s lead, tucking home at the back post from Pavlidis’ cross for the fourth before netting from close range.
Nikko Boxall brought down Di Maria in stoppage time and the Argentine World Cup winner beat Garrow from the spot again to wrap up Benfica’s emphatic triumph.
Later on Friday (today, local time), German giants Bayern Munich take on Argentine outfit Boca Juniors in the other Group C match.
On Tuesday (local time), the Mamelodi Sundowns’ game against Ulsan HD was suspended just before kickoff for over an hour due to a weather alert.
RB Salzburg’s match against Pachuca was held up in the second half for 97 minutes because of a storm the next day.
Then a day later, Palmeiras’ game against Al Ahly was paused for nearly 45 minutes in the second half because of a nearby storm.
Common public safety protocols in the US mandate that outdoor sports events are suspended for at least 30 minutes when lightning is seen or thunder heard.