Following back-to-back victories over Newcastle and Everton, the defeat to relegation-rivals Villa has halted the Black Cats' charge to safety as they now sit just five points above 18th-place Wigan.
Gardner feels the squad may have become complacent after their sharp upturn in form following new manager Paolo Di Canio's appointment, and the recent loss was a needed "kick up the backside."
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"For sure, it won’t happen again. Maybe it’s something we needed to kick us back into touch, but we need to get points and make sure we get over the line."
Gardner, who returned from suspension against his former side, refutes suggestions the club took their foot off the gas but believes there must be renewed concentration ahead of the final furlong.
He said: "It’s not as if we’ve been getting carried away, thinking we’re this or that. We can’t dwell on Monday now - we have three games left, two of those at home and those games are cup finals for us.
"We have to give every last little bit of energy in our bodies to get results – we want to finish the season on a high and hopefully get some good points out of those last three games.
"Forty points is the mark everyone wants to get to. Stoke will maybe be a bit more relaxed and we need to start like a house on fire.
"We have to give the fans exactly what they expect and I’m sure the gaffer will be kicking us up the backside as well."