The sisters — whose nephew Psalm turned five this week — posed up for photos and videos during the celebratory occasion.

It comes after the supermodel insisted that there’s never been a sibling rivalry over ‘who’s prettier.’

Kendall and Kylie Jenner showed off their figures in tight dresses during a surprise appearance at Marquee Las Vegas ‘ Summer Kickoff event

Kylie slipped her curves into a skintight red PVC dress while Kendall opted for a strapless black mini dress

Taking to Instagram, the sisters — Kendall, 28, and Kylie, 26 — shared various outtakes from the soiree

The family members were photo-ready as they delighted unsuspecting fans who were partying at the pool and bar.

Kylie put on a busty display in her dress, which was low-cut and featured spaghetti-thin straps.

She complemented the 𝑠e𝑥y number with a pair of nude, backless heels with perspex straps.

The mother-of-two’s bouncy brunette locks were arranged in a center part and fluffy barrel curls.

And the makeup mogul’s visage was beautifully made up, with her cheeks blushed and her pout coated in a mauve lipstick with darker liner.

For her part, Kendall wowed in a layered, straight-cut top and matching teeny skirt.

She punctuated the simple and sophisticated outfit with strappy black heels.

The runway regular wore her dark hair loose, also style in a middle part as it flowed down her back.

Kylie shared an Instagram grid post with multiple photos from the event

Engaging her 400 million followers, she wrote in the caption, ‘sister work day @drinksprinter @drink818’

The sisters showed their playful side in images from the pool party

The older Jenner had a pair of narrow black sunglasses set atop her head in the series of photos and video clips.

And the Kylie Cosmetics founder also wore a pair of glossy, onyx shades in some outtakes.

Kylie shared an Instagram grid post with multiple photos from the event.

Engaging her 400 million followers, she wrote in the caption, ‘sister work day @drinksprinter @drink818.’

The bombshell uploaded various closeup shots with her big sister.

The official Marquee Instagram account shared footage from the fun day, writing in the caption, ‘Pool season has officially arrived at #MarqueeDayclub’s Summer Kickoff.’

It was added that ‘@kendalljenner and @kyliejenner surprised the party and kept the vibes going strong’ with their beverages.

The sisters posed up for photos and videos during the celebratory occasion

Kendall was spotted holding a bottle of her 818 Tequila while Kylie held a green can of her vodka-mixed drink

This week Kendall opened up to Vogue about the dynamic between her and Kylie, whose parents are Kris Jenner and Caitlin (nee Bruce) Jenner.

‘Even with my little sister — the biggest thing we would fight over was the TV remote. There was never that who’s-better-dressed, who’s-prettier thing. It was always: You’re you, I’m me,’ she told the fashion magazine.

‘I’ve never thought of my career as a competition, and that’s thanks to awesome sisters. I really do me, and if you don’t like it, that’s okay. But I trust that me being the most authentic version of myself will get me to the places it needs to get me,’ she added.

Kendall and Kylie launched their careers as teenagers with Kendall + Kylie collaborations with PacSun, Topshop, Gillette, Steve Madden, Pascal Mouawad’s Glamhouse, and Glu Mobile.