The eight-wicket victory, coupled with Smethwick’s defeat to Pelsall, saw Dartmouth secure top spot in Group Two and set up a last-four encounter with Shifnal on Saturday week.
Omar, the brother of England star Moeen, starred with both ball and bat as Harborne were simply overpowered.
Batting first, the hosts quickly found themselves reduced to 15-4 and then 64-7, with only a defiant 52 from former Dartmouth captain Guriq Randhawa – supported by Jonathan Boukhobza’s 42 – helping them post a moderate total of 172. Omar finished with figures of 3-26, while Manraj Johal and Drew Malek both picked up two wickets apiece.
At the midway point, Harborne’s bowlers might have felt they at least had something to bowl at, but Ali quickly extinguished any hope – blasting an unbeaten 110 from just 63 balls as Dartmouth required just 23.3 overs to chase down the target.
Omar’s innings, which followed on from a similarly impressive 95 against Walsall the previous week, took his tally for the season to 529 runs.
Smethwick, who were already facing an uphill struggle to overhaul Dartmouth, saw their hopes of topping the group disappear completely as they were beaten by seven wickets at Pelsall.
Put in to bat, the visitors quickly found themselves in big trouble as Pelsall’s opening pair, Tom Boyd and Todd Henderson, wreaked havoc.
At one stage Smethwick were 36-7 before Hamza Ahmed (70) steadied the ship, ably supported by Karamjot Singh (35) and Nasser Ahmed (23).
Their efforts helped the visitors post 165 as Boyd and Henderson finished with three wickets each. Henderson then hit an unbeaten 48 to help Pelsall chase down the target in the space of just 30 overs.
Smethwick may now struggle to hold on to second place in the group after Walsall recorded a four-wicket win at Himely.
Skipper Oli Westbury’s 68 was the highlight of the home side’s 165-7 from 40 overs, Jordan Bulpitt finishing with figures of 3-15 for the visitors.
Walsall’s reply began unsteadily and the match looked in the balance when James Middleton was the fourth wicket to fall, with 100 runs still required.
But Billy-Jo Cox held his nerve to hit 84 from 94 balls and steer his team home, with the help of Jimmy Howell (21) and Luke Stynes (21 not out).
Back-to-back defeats have ended any hopes Halesowen had of qualifying from Group Four. Saturday’s loss, against a previously winless Bromsgrove outfit, was particularly disappointing.
Harry Baddams’ unbeaten 80 was the highlight of Halesowen’s total of 188-8 from their 40 overs. Bromsgrove’s Alex Milton then hit 78 from 76 balls as the hosts got home with four balls and wickets to spare.
Kidderminster have also been guilty of going off the boil at the wrong time and they too suffered a second successive defeat as they went down by 70 runs at Ombersley.
Josh Dell’s 106 helped the hosts compile 223-3 from their 40 overs. In reply, Kidderminster simply could not keep up with the rate, Andrew Kimberlin top scoring with 49 from 81 balls as they finished on 153-6.
Wolverhampton are up to second in Group One after a four-wicket win over Wem, but are unable to catch leaders Shifnal.