The Belgian champions marched into the Philips Stadion and beat PSV 3-1 in their first UEFA Champions League outing in their 128-year history, thanks to goals from Promise David, Anouar Ait El Hadj, and Kevin Mac Allister.
Following the game, manager Peter Bosz acknowledged that his team simply weren't good enough. "And if you're not good enough, you need luck on your side, and we didn't have that," Bosz told Ziggo Sport.
"You get a few chances in the first half and you don't take them. Then you concede a penalty, but all in all, I think they deserved to win," said Bosz, who did not get angry at his players.
"If the lads don't do their best, I can get angry, but that wasn't the case. It wasn't good enough, and we have to learn from this, just as we have learned from our first game in other years. We have to make sure we raise our level."
Extremely difficult schedule
PSV lost their UEFA Champions League opener for the fifth time running and have a mammoth schedule ahead of them with home games against Atletico Madrid, Napoli, and Bayern Munich, and away games at Bayer Leverkusen, Liverpool, Newcastle United, and Olympiacos.
Despite losing what looks like the most winnable game, Bosz stays calm - "This is the third year I've played in the Champions League with PSV and the third time we've lost the first match. The previous times, things turned out well afterwards."
'Afraid to get the ball'
Midfielder Joey Veerman had different criticisms for his team. "It seemed as if we were afraid to ask for the ball. Then you end up with people running with the ball, and it all takes far too long. It just wasn't good today," said Veerman.
American striker Ricardo Pepi had a share in two of Union Saint-Gilloise's three goals, but those weren't what brought PSV down on Tuesday.
"Those are personal mistakes. That can happen; everyone makes them. We have to solve it as a team."
Veerman was less sympathetic towards fellow midfielder Ismael Saibari, who missed two massive opportunities at getting PSV on the scoreboard, one of which was in front of an open goal: "That should not happen in the Champions League."