O'Riley injured in Brighton's EFL Cup win over Crawley as Premier League clubs avoid upset
The Denmark midfielder went straight into the starting lineup a day after completing his 25 million pound ($33.15 million) move from Celtic to the Premier League but lasted only nine minutes.
He was helped off after treatment to an apparent left ankle injury following a heavy tackle.
Simon Adingra slotted the Seagulls ahead in the 31st and Brighton, second in the Premier League after two games, finished with a flourish as Jeremy Sarmiento, Adam Webster and Mark O'Mahony scored in the second half.
Their third win in three games was another boost for Brighton ahead of a tough trip to Arsenal in the league next Saturday.
There were no upsets for any of the Premier League sides in action with Fulham, Crystal Palace and Leicester City all seeing off lower-ranked opponents without drama.
Struggling Everton were made to sweat at home against fourth tier Doncaster Rovers, who could even feel unfortunate to go in goalless at the break, before Sean Dyche's side ran out as 3-0 winners.
After shipping seven goals without reply in the Premier League, Everton finally found the net through Tim Iroegbunam in the 53rd, new signing Iliman Ndiaye in the 74th and Beto in the 83rd after missing an earlier chance.
Fulham were 2-0 away winners at League One Birmingham City, Palace swept past Norwich City 4-0 and promoted Leicester also walloped League Two Tranmere Rovers 4-0 for their first win of the season.
The second round is the start of the competition for those Premier League clubs not playing in Europe this season, with the likes of Manchester City, Chelsea and Arsenal joining in the third round.
Stoke City were among the night's high scorers, the Championship side winning 5-0 at second tier rivals Middlesbrough.
Dutch winger Million Manhoef scored two of those goals within seven minutes of coming on as a second half substitute.
Sheffield Wednesday won 5-1 at Grimsby Town while Preston North End beat Harrogate 5-0.
Queens Park Rangers beat Championship rivals Luton Town 4-1 on penalties after ending the game 1-1 to go through to the third round.