Former Derry City midfielder Aaron McEneff was on target as Shamrock Rovers defeated the 10-man Candystripes 2-0 in Dublin.
Dylan Watts capitalised on an Eoin Toal error to open the scoring for the home side in the 29th minute.
McEneff sealed the win 11 minutes from time with a well-executed 'Panenka' penalty after a Toal handball.
Jamie McDonagh was sent off in the 85th minute for a late challenge near the touchline on Trevor Clarke.
City had won their first match of the Premier Division season against UCD last week, while the result made it two wins from two for Rovers.
It was a deserved victory at the Tallaght Stadium for Stephen Bradley's team, who finished last season in third place in the table, but they were made to work hard by Declan Devine's youthful Derry line-up.
Watts' opening goal came when a Ronan Finn header into the box wasn't cleared properly by Toal and the 21-year-old got a good connection on his shot to finish well.
McEneff then showed a lot of nerve from the spot against the side he left in November when a spot-kick was awarded after Toal blocked an Orhan Vojic shot with his hand.
The midfielder placed a chipped effort down the middle which deceived Scottish keeper Peter Cherrie and made sure of the victory for Rovers.
McDonagh's sending off came after he had initially challenged Sean Kavanagh but then he was reckless with a tackle on Clarke and received a straight red card.
Aaron Greene had the first chance of the game but his left-foot shot in the eighth minute was saved by Cherrie.
The striker thought he had opened the scoring two minutes later, but his goal at the back post was ruled out for offside.
Despite their hard work, the visitors created very few goalscoring opportunities, with a 40-yard effort from Eoghan Stokes that was deflected wide the closest they came.
The Brandywell outfit are at home to Waterford on Monday then face a difficult trip to Cork City next Friday.