Middlesbrough boss Tony Mowbray says Chelsea's opening goal in Wednesday's 2-0 FA Cup loss was the crucial blow to his side's hopes of staying in the tie.
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Ramires' strike took a deflection off Fernando Torres to beat Jason Steele, before Victor Moses settled the match with Chelsea's second.
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"We worked extremely hard, the team shape was good but we were undone by their first," Mowbray said..
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They have won just three games in 2013 - against Leeds in the league, and Aldershot and Hastings in the FA Cup Boro have conceded 19 goals and scored seven since the start of January.
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"You could feel their quality but we stood up to it well."
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Mowbray added: "It's good for our players to play against that quality, and we didn't just sit back and defend but they're hard to break down."
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The visit of the Premier League side is followed by that of Cardiff City, who are on course to join the Blues in the top tier next season.
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Boro are on a run of just one win in nine league games after Saturday's 2-1 home defeat by Millwall, having picked up only four points from a possible 27 in 2013.
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"We are doing a lot of things right but we just need a break, we have to keep working," Mowbray added,
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"Let's hope against Cardiff that break comes and we get the points."