Republic of Ireland internationals Conor Hourihane and Graham Burke were on target in Carabao Cup victories for Aston Villa and Preston respectively.
Villa were made to work hard for their 1-0 victory over League Two Yeovil at Huish Park. Alex Fisher missed a penalty for the Glovers before Cork midfielder Hourihane claimed Villa's 77th-minute winner.
Fellow Ireland international Graham Burke scored on his first competitive start for Preston. The former Shamrock Rovers man got the final goal in a 3-1 win over League Two Morecambe.
Championship sides Middlesbrough and Nottingham Forest both survived scares among a host of first-round ties to be settled on penalties
Middlesbrough were held 3-3 over 90 minutes by League Two Notts County in an eventful game at the Riverside Stadium but prevailed 4-3 on spot-kicks.
Boro trailed three times in normal time but two goals from Ashley Fletcher and another from Enes Mahmutovic cancelled out a Jon Stead double and Tom Crawford strike.
With extra-time no longer played at this stage of the competition, Andy Lonergan then made two saves in the shoot-out.
Nottingham Forest, reduced to 10 men after the first-half sending off of goalkeeper Jordan Smith, looked to be heading out at the City Ground until Matty Cash made it 1-1 against League Two Bury with a stoppage-time equaliser.
The Shakers had led since a second-minute strike from Irish defender Eoghan O'Connell, recently of Celtic and cousin of former Ireland rugby captain Paul. Forest won 10-9 on penalties.
Bristol City did go out to lower division opposition, falling 1-0 to League One Plymouth at Ashton Gate. Yann Songo'o claimed the only goal.
Blackburn had no such worries as they thrashed Carlisle 5-1. Adam Armstrong and Bradley Dack both got on the scoresheet twice for Rovers with Kasey Palmer also on target.
West Brom also found things far from straightforward against League One Luton but eventually came through at The Hawthorns with a 62nd-minute goal from Oliver Burke.
Reading saw off Birmingham 2-0 in another Championship meeting, Yakou Meite and John Swift netting their goals.
Leeds prevailed 2-1 in their all-Championship clash with Bolton at Elland Road. Patrick Bamford and Saiz Samuel struck before Erhun Otzumer replied.