Dundee United were beaten 1-0 by Hearts in the Scottish Premiership on Sunday as new manager Mixu Paatelainen endured a losing start to his reign at Tannadice Park.
The former Finland international was appointed Jackie McNamara's replacement this week, but failed to spark an instant revival in fortunes Juanma struck from the spot 15 minutes in and the hosts finished with 10 men.
Rock-bottom United had failed to keep a clean sheet at home in the league prior to the clash and that run continued after Sam Nicholson was brought down by Blair Spittal inside the area.
Juanma found the bottom-left corner from the spot in what proved to be the game's decisive moment.
Aaron Kuhl went close with a free-kick, while Billy McKay saw an effort saved before Spittal's late dismissal compounded a disappointing afternoon for Paatelainen and United.
Having been booked for a foul two minutes from time, Spittal was again penalised for a similar offence inside injury time as United remain winless in the league since the second weekend of the season.
Hearts move third after their first win in six league matches.
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