Spurs dropped to fourth in the Premier League after a lacklustre display at White Hart Lane against Fulham was settled by a goal from former White Hart Lane favourite Dimitar Berbatov.
It was a second straight league defeat, and allowed rivals Arsenal to close the gap to just four points, with a match in hand and far superior goal difference.
The Iceland midfielder, though, claims Spurs must concentrate on getting themselves back in form over the final eight league games - and then it will not matter what any other sides do.
"We just need to pick ourselves up, stay together and perform well until the end of the season," said Sigurdsson, who started his second match of the week after their Europa League tie at Inter Milan.
"It (a top-four finish) is in our hands and we are in a good position to make sure we get the Champions League spot.
"We showed during the season that we are more than capable.
"Even though (we've had) a couple of bad results, we won't start doubting ourselves.
"It's down to us now and we have just got to make sure we are playing the way we've been playing throughout the season."
Manager Andre Villas-Boas made the expected changes after the 4-1 defeat against Inter, which still saw his side progress to the quarter-finals on the away goals rule.
Wales international Gareth Bale was suspended for the European tie, and Sigurdsson felt fatigue should not just be used to explain why Spurs failed to deliver the required performance yesterday.
"I don't want to be making excuses, but the 120 minutes probably played a bit of a part from Thursday night and also the travelling, but we could have played better even if we were tired," he said.
"It could have been a factor, but we have to make sure we are fresh and ready for the next game.
"The lads can pick themselves up. We have got the determination to get into the Champions League.
"We showed at Arsenal at home that we can beat anyone here so there will be a good few games coming up and hopefully we can get a few points."
Sigurdsson feels the Spurs squad can regroup over the international break.
"We would have liked another game in a few days to make things right and get another three points on the table, which is important, but maybe it is a good thing because we can go away and reflect on what we have been doing in the past few games and make it right," he said.
Tottenham blew the chance to secure automatic Champions League football last season over the run-in, as Arsenal overtook them before Chelsea's penalty shoot-out win in the final in Munich saw them drop into the Europa League.
However, Villas-Boas maintains that, with fixtures against both Chelsea and Manchester City still to come, there is no reason to press the panic button just yet.
"The most important thing is that we have enough games - important games - that can enable us to get out of that situation," the Portuguese coach said.
"This result didn't go our way, In Milan it didn't go our way, Liverpool didn't go our way, but there were still some positive things for us to hang on to try to change these results that we have been getting."
Tottenham have several first-team players away on international duty, despite both winger Aaron Lennon (groin and hamstring) and captain Michael Dawson (hamstring) being ruled out of England's double-header with San Marino and Montenegro.
Bale, meanwhile, suffered a knock to his ankle in the second half yesterday, but is expected to still feature for Wales in their World Cup qualifiers, which include a clash against Scotland at Hampden Park on Friday night.