Jabeur came from 6-3 down in the tiebreaker, then broke the 24th-seeded Mertens in the final game of the second set when her opponent double-faulted on match point on No. 1 Court.
"It's my kind of thing to express a little bit my stress during the match, doing funny things with the football or anything just helps me connect with the crowd,'' Jabeur said of her ball skills, like when she chased down and headed away a lob from Mertens that went long. "Be myself on the court really is very, very important.''
She improved to 9-0 this season on grass, which includes winning the Berlin Open last month.
Just over a year ago, she became the first Arab woman to win a singles title on the elite women's tennis tour when she lifted the trophy in Birmingham -- also a grass-court tournament.
"I love playing on grass, I love the connection between the nature and me, so hopefully it will continue this way for me and maybe through the finals," Jabeur said.
Shaking off the disappointment of a first-round loss at the French Open, Jabeur's goals are "very high" at the All England Club.
"No matter who's coming, I'm going to build the fight, I'm going to fight 'til the end because I really want the title,'' said Jabeur.
Jabeur described her match, particularly the tiebreaker, as "10 out of 10 stressful" but said that she's coping better now.
"I am breathing better. I'm expressing more my feelings before the matches. That helps me, like, really play the game that I want to play,'' she said.
Jabeur will face unseeded Marie Bouzkova, with both players trying to reach their first Grand Slam semifinal.
She'll next face not another high-seeded opponent, but Jule Niemeier, 22, who is making her All England Club debut, in an all-German showdown for a place in the semifinals.
Heading into the second week at Wimbledon, only two of the top 15 seeds remain in the women's draw, which has just one Grand Slam champion -- Simona Halep -- left.
"I always believed that at one point I can show what I can do,'' said the 103rd-ranked Maria, who ousted fourth-seeded Maria Sakkari in the third round. "I'm happy that today, I mean, I came back when I was down, so I'm proud of myself.''
Halep is the last Grand Slam champion standing on the women's side. The 16th-seeded Romanian won at Wimbledon in 2019 and at the French Open the year before that. She faces fourth-seeded Paula Badosa in the fourth round on Monday.
The 97th-ranked Niemeier advanced by beating Heather Watson 6-2, 6-4 on Centre Court in just her second Grand Slam tournament. The German had eliminated second-seeded Anett Kontaveit in the second round.
"I came here, I just wanted to win my first round after losing in Paris,'' said Niemeier, who lost in the first round at Roland Garros. "Now, being in the quarterfinal in Wimbledon, I don't know, I'm speechless. It just feels not real. Yeah, I'm just so happy."
Bouzkova, of the Czech Republic, reached her first Grand Slam quarterfinal by beating Caroline Garcia of France 7-5, 6-2 as the traditional day of rest on the middle Sunday at the All England Club is no more.
"There's no reason why not to keep this going. Kind of believing in myself right now,'' said Bouzkova, who withdrew from the French Open after testing positive for COVID-19. "Yeah, I just going to go all out again in the quarterfinals.''
The Associated Press contributed to this report.