Alex Blake and Fidel Edwards produced spectacular T20 Blast performances with bat and ball in stunning wins for Birmingham Bears and Kent Spitfires.
West Indian paceman Edwards took three wickets in the first over at Edgbaston as Bears reduced Leicestershire to 2-3 before winning by seven wickets.
Kent batsman Blake hit successive sixes to seal a two-wicket win against Hampshire with just a ball to spare.
Elsewhere, a Glenn Maxwell-inspired Lancashire beat Durham by 72 runs.
Big crowds filled all three grounds a week on from England's dramatic World Cup final triumph with just under 10,000 at Hampshire's Ageas Bowl, their largest T20 Blast attendance for two years.
Edwards only finalised his loan to Birmingham Bears from Hampshire on Friday.
The 37-year-old, who is without a white-ball contract at Hampshire, was on the money from the start as Neil Dexter was bowled by a beauty that clipped the top of off stump.
Two balls later, fellow opener Mark Cosgrove had his stumps rearranged by an inswinger before Arron Lilley was caught by Adam Hose of the last ball to leave Leicestershire in strife.
Foxes found little joy from the rest of their innings despite battling efforts from Harry Dearden (27) and Colin Ackermann (26) before Edwards returned to dismiss Callum Parkinson and claim 4-22.
Spinners Jeetan Patel (2-24) and Ashton Agar (1-25) restricted Leicestershire to just 115-9.
In reply, Australia all-rounder Agar's 41 not out off 28 balls featured five fours and a six as the hosts coasted to victory on 117-3 with 31 balls to spare.
Bears registered their first win after rain washed out their opening fixture at Worcestershire on Friday. It was the same story for Leicestershire that night, who had their opening game at home to Lancashire abandoned.
Like a lot of matches at the 50-over World Cup, a used pitch at the Ageas Bowl produced a relatively low-scoring thriller between Hampshire and Kent.
The hosts won the toss and batted first after the weather scuppered their home game against Sussex on Friday.
Only skipper James Vince, returning to county colours for the first time since being part of England's World Cup win, could find any timing with 51 off 35 balls.
The hosts posted 145-5 as two wickets apiece from Hardus Viljoen (2-20) and Freddie Klaasen (2-27) stemmed the run-scoring.
But chasing proved far from simple as Kent were reduced to 34-3 in the Powerplay and after 10 overs were just 58-4.
Alex Blake hit four sixes to guide Kent to victory against Hampshire
Enter Blake, who in 2015 on the same ground produced a match-winning 71 not out off just 31 balls.
He was to be Hampshire's nemesis once more despite Kent needing 16 to win off the final over from left-armer Chris Wood.
Blake took two off the first two balls, before a Wood yorker made the equation 12 off three balls.
Blake was unnerved though smashing successive sixes to win the game with one ball remaining and finish unbeaten on 57 off 38 balls in Kent's 146-8.
It was a second win in as many days for Kent, who handsomely beat Somerset by 41 runs at Canterbury on Saturday.
Old Trafford also welcomed a healthy crowd as Lancashire played at home for the first time in this year's competition.
The match featured a first-time trial of a hybrid wicket of part-grass, part-astro turf which will potentially feature in The Hundred next season.
Despite that Lancashire had no problems batting first and scoring quick runs.
Australia all-rounder Glenn Maxwell struck three fours and four sixes in his 33-ball 58 while Steven Croft made an unbeaten 65 as the hosts made an imposing 189-3.
Maxwell and Croft added 97 for the second wicket with the latter hitting four fours and two sixes.
Lancashire and Durham played on a hybrid wicket at Old Trafford as part of a trial
Durham never threatened in reply despite opener Scott Steel's 58 from 46 balls. He lacked any real support with 12 from Alex Lees the next highest score.
Matt Parkinson bagged 3-30 with his leg-spin as Durham were dismissed for just 117 in the 17th over.
Durham have won one and lost one after their first two games while Lancashire are up and running after a no result at Leicestershire on Friday.
T20 Blast action returns on Tuesday evening with two more games.
Leicestershire Foxes host Yorkshire Vikings in the North Group at Grace Road while there's set to a bumper crowd at The Oval as Surrey host Middlesex in the London Derby.
Both matches start at 18:30 BST and there will live text coverage and ball-by-ball radio commentary on the BBC Sport website and app.