The world No.273 lost 6-4, 7-6 against Peniston at St. George's Hill Lawn Tennis Club, scuppering his chances of maintaining an unbeaten record as Peniston's victory blew Pool B wide open.
Ward was in no mood to talk in Weybridge and reckons the British No.14 played 'way above his normal level' to eliminate the gap at the summit of the group.
"He played way above his normal level and sometimes things don't go your way, and today was one of them," Ward, 33, said.
"Obviously in this format, none of these guys have any pressure playing against me.
"So they just come out, go for everything and on some days, it comes off and there's not much you can do.
"Not really [rustiness playing a factor] because I'd just won three matches already this week."
Ward is one of 24 leading players duelling it out in the widely-billed Premier League of tennis, competing against a glittering array of talent including Harriet Dart and Eden Silva in the women's draw and Liam Broady and Anton Matusevich in the men's.
The innovative format was devised by Andy Murray's coach, Jamie Delgado, with players on Classic Week being split into two boxes of six ahead of finals weekend on August 15th and 16th.
Emma Raducanu reckons age is just a number after her first defeat of the week.
The 17-year-old had embarked on a thrilling winning streak at St. George's but was beaten by fellow high-flyer Jodie Burrage in a super tie-break.
The precocious Raducanu lost the first set 6-3 but restored parity with a classy 6-2 win in the second, before the British No.7 proved too strong to win 10-6 in the decider.
Burrage is four years Raducanu's senior but the Toronto-born prodigy says that's no excuse for her defeat.
"It's good that I'm younger, but I like to measure myself about the best out there in the world," she said.
"I always aspire to be better and I don't think that age has a real limit on it.
"I thought I was quite flat from the start and she was quite dominant throughout the match while I was playing quite passively.
"It wasn't the best tennis but I've got a lot to learn from about how she played and match situations.
"Physically, I've got a lot of developing to do in terms of strength, as I break down a lot easier as matches go on and in points, so from that side age does play a big factor in it.
"I'm still quite weak but it can only get better."
Peniston's win in the men's draw makes things spicy in Pool B and there was also a triumph for 18-year-old Arthur Fery, who toppled Henry Patten 10-4 in a super tie-break.
Underdog Patten had taken the first set before Fery drew level with a 6-3 win, with the young star then showing all his precocity in the decider to beat a man four years his senior.
Julian Cash hit the jackpot for the first time this week as he beat Luke Johnson in a pulsating super tie-break triumph, winning 10-6 to outline his resilience after three consecutive defeats.
There was drama in Pool A as Matusevich got stuck in traffic and was forced to miss his match against Broady.
And that meant on-site alternate player Tom Hands got the call-up against the British No.8, delivering a valiant performance despite the short notice but losing 7-5, 6-3.
Hands had to buy a new, non-branded shirt to comply with tournament regulations and said: "I was just excited to be able to compete and play matches against high-ranked players.
"But I had to nip to the shop to buy a new shirt so I could actually play!
"I felt like I played pretty well - I obviously wasn't as prepared as I could have been if I'd known I was playing, but it's always really nice to play someone of Liam's standard as that doesn't come around that often for me. It was a pleasure to play."
Dan Cox picked up a brilliant third win in a row against Alastair Gray, while Mark Whitehouse secured his maiden triumph of the week over Billy Harris - who had beaten Broady the night before - with a 10-8 super tie-break win.
Burrage reigns supreme in Pool B of the women's draw after her win over Raducanu and there was also a win for the impressive Emily Appleton, who beat Nadia Rawson 6-1 6-3 to further outline her credentials.
And Sarah Beth Grey toppled an unfortunate Eliz Maloney in the other game in that group in a narrow 11-9 super tie-break win.
Dart hit the bullseye once more to consolidate her lead at the top of Pool A but also took a super tie-break to get over the line.
The British No.3 beat Silva 10-7 in the decider, while other high-flyer Broady won her super tie-break 10-8 against Freya Christie late in the day.
And Sonay Kartal came from behind to win her super tie-break 10-3 against Emily Arbuthnott in the battle at the bottom, on a day where five of the six women's matches went the distance.