The 58-year-old coach praised his players for their performance at the Estadio da Luz, but believes that a place in the last four is still up for grabs.
"It was a great game against a great team, which hampered most of our first quarter-hour," Jesus told reporters.
"But our players believe in what they do and we believed we were going to go around the result.
"This result does not guarantee us anything, everything is open."
The second leg takes place at St James' Park on Thursday.