In 2021 Ebro River was ridden in most of his races by James Doyle. The colt made his track debut on 13 April in a novice race (for horses with no more than two previous wins) over five furlongs at Newmarket Racecourse in which he started at odds of 11/1 and finished sixth after becoming upset in the starting stalls and then struggling to obtain a clear run in the closing stages.[6] On 15 May at Doncaster Racecourse he started 13/8 second favourite for a novice race over the same distance on soft ground when he was ridden by David Egan and recorded his first victory as he recovered from a poor start to take the lead two furlongs out and won by a length from Kyber Crystal with the pair finishing six lengths clear of the other six runners.[7] Twelve days after his success at Doncaster Ebro River was stepped up in class for the Listed National Stakes at Sandown Park and started the 4/1 third choice in the betting behind Navello and Chipotle in a seven-runner field. With Doyle in the saddle, he took the lead approaching the final furlong and despite hanging to the left in the closing stages he drew clear of his opponents to win by three and a quarter lengths.[8] Hugo Palmer, who was unable to be present at the course after being sy=tuck in traffic said: "He's looked very smart from the first day he came in. He's obviously still a bit babyish and has a few crinkles to iron out – how we do that, I'm not sure. He'll be fine on any ground and it isn't a surprise he's so precocious... This horse will get a mile in time, but we'll gradually step him up as the season progresses. He's got some growing up to do."[9]
At Royal Ascot on 15 June Ebro River was moved in class and distance for the Group 2 Coventry Stakes over six furlongs when he took the lead approaching the final furlong but was overtaken in the closing stages and finished fifth behind Berkshire Shadow, beaten two and a quarter lengths by the winner. He next appeared Newmarket 23 days later when he came home fourth behind Lusail, Asymmetric and Sam Maximus in the July Stakes. In the Richmond Stakes at Goodwood Racecourse on 29 July he finished fourth again, but was beaten less than a length by the winner Asymmetric. Despite three consecutive defeats the colt was promoted in class again when he was sent to Ireland to contest the Group 1 Phoenix Stakes at the Curragh on 8 August when he was ridden by Shane Foley and started at odds of 12/1. The Railway Stakes winner Go Bears Go started favourite while the other Group race winner in the eight-runner field was Castle Star (Marble Hill Stakes). In a change of tactics Ebro River took the lead soon after the start and set the pace from The Entertainer. He was headed by Dr Zempf and Go Bears Go approaching the final furlong but rallied to regain the advantage and won by three quarters of a length and a head from the aforementioned colts.[10] After the race Foley said "We just said beforehand we wouldn't mind changing the tactics a bit. We'd been dropping him in but there didn't look to be much pace today and with that tailwind it can be hard to get them back up front. He'd been doing things wrong. He'd been keen and quite awkward. Hugo had in his head he wanted to go forward today and it was an ideal day to do it. He had the draw for it. I had a willing partner and he kept pulling out more."[11]
On 12 September Ebro River returned to Ireland for the Group 1 National Stakes over seven furlongs at the Curragh and started the 13/2 third choice in the betting. He took the lead from the start and maintained his advantage until he was overtaken inside the final furlong and finished third behind Native Trail and Point Lonsdale.[12] On his final run of the year he was sent to France to contest the Group 1 Prix Jean-Luc Lagardère over 1400 metres on heavy ground at Longchamp Racecourse on 3 October. He was among the leaders for most of the way but faded badly in the closing stages and came home eighth of the nine runners behind Angel Bleu.[13]
