Mekhissi, a three-time Olympic and two-time world medallist, was imperious as he eased to a fourth victory in the 3000m steeplechase in 8min 31.66sec, having already won the discipline three times (2010, 2012, 2016) and the 1500m once (2014).
Mekhissi, who was controversially stripped of the 2014 steeplechase title for having stripped off his singlet before he crossed the finish line in first place, has the chance for an unprecedented sixth gold when he competes in Saturday's 5000m.
"It was tough today," he said. "To keep that level over 10 years is not easy.
"I really wanted to defend my title, but there was a lot of stress and there's no doubt it was my most emotional race.
"I'm extremely proud. To be a five-time European champion is historic."
Reigning world champions Ramil Guliyev and Karsten Warholm had earlier lit up the track to win the 200m and 400m hurdles, while Greece's Ekaterina Stefanidi showed all her nous to defend her European pole vault title.
Turkey's Guliyev justified his decision to sit out the 100m by absolutely dominating the 200m.
The Azeri-born sprinter led from gun to tape, attacking the bend and powering his way through the line in a new championship record of 19.76sec, smashing the previous best of 19.85 set by Greek Konstadinos Kederis in Munich in 2002.
The time also took Guliyev to second on the European all-time 200m list behind Italian Pietro Mennea's long-standing mark of 19.72, set at altitude in Mexico in 1979.
Norway's Warholm, a surprise world champion in the 400m hurdles in London last year, survived a little blip coming off the final bend to add the European crown to his accolades, winning in 47.64sec.
The 22-year-old charged out of his blocks, the whip-like action of his lead left leg propelling him past Ludvy Vaillant of France in the lane outside him within metres.
But defending champion Yasmani Copello, the Cuban-born Turk, two lanes inside Warholm, stuck with the Norwegian and came into the home straight neck and neck.
Faced with two hurdles to the line, Warholm kept his nerve as Copello faltered on the last in the strength-sapping event. It was just enough to hand the Norwegian the advantage, and also kept him on track for an ambitious bid for a double, having already qualified for Friday's 400m flat final.
"After my world title I am now European champion now! It sounds like where I should be," Warholm said. "I had just enough to give on the last 100m."
- Imperious Stefanidi -
Stefanidi, defending world, Olympic and European champion, claimed a second continental title by clearing a championship record of 4.85m. Teammate Nikoleta Kiriakopoulou took silver with 4.80m to add to her bronze from 2012, with Briton Holly Bradshaw claiming bronze (4.75).
The large partisan crowd at Berlin's Olympic Stadium were also treated to a show in the men's javelin, Germany's Olympic champion Thomas Roheler claiming gold with 89.47m from compatriot Andreas Hoffmann.
No sooner had Mekhissi wrapped up his steeplechase victory than Roehler was diving into the pool of the steeple's water obstacle in celebration.
Belgian Nafissatou Thiam's bid to add European glory to her world and Olympic heptathlon titles will seemingly go to the wire thanks to Britain's Katarina Johnson-Thompson.
A new heptathlon championship best of 22.88sec by Johnson-Thompson in the 200m saw her take the overnight lead on 4,017 points, 87 ahead of Thiam with the long jump, javelin and 800m to come on Friday.
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