Northern Ireland international Ward slammed home a Craig Forsyth cross after 61 minutes to give McClaren his fourth win in six games since taking the hot seat from Nigel Clough.
In contrast, Eddie Howe's promoted side have only won once in nine games and have now lost back-to-back matches at home.
The Rams have been in good form since the former England boss took over in October and his team started brightly.
Youngster Will Hughes, thought to have attracted strong interest from Liverpool, guided a neat through ball to Ward after 11 minutes but the winger could only shoot straight at Lee Camp.
Camp, who started his career at Pride Park before leaving in 2009, was soon back in action, keeping out a volleyed effort from Chris Martin after 16 minutes.
Bournemouth record signing Tokelo Rantie got off the mark for the Cherries in their last game against Burnley and the South African went close with 19 minutes on the clock.
The striker latched onto a defence splitting pass from Lewis Grabban before turning inside Jake Buxton but could not find a way past Lee Grant.
It was turning into a busy afternoon for Grant's opposite number Camp with the keeper first saving again from Ward before tipping a stinging drive from Simon Dawkins over the bar just before the break.
South-coast Bournemouth had only picked up two points out of 12 prior to kick-off but came out of the changing rooms attacking.
Brett Pitman should have done better with his shot after good work from Grabban but blazed high into the stand when unmarked.
Former Bristol City man Pitman then flicked on for Marc Pugh to go clean through on goal but the winger could not get his shot away.
Ward's fifth of the campaign came just after the hour when left-back Forsyth delivered a pin-point ball into the box for Ward to take a touch and shoot past Camp.
After the deadlock had been broken a desperate Bournemouth, who had Steve Cook stretchered off in the dying moments and have now lost four home games this campaign, pushed for the equaliser.
Eunan O'Kane headed over after 73 minutes before substitute Matt Ritchie, making his first appearance of the season, saw two efforts whistle past the post.
With 10 minutes left on the clock, Wes Thomas set up fellow sub Ryan Fraser but the midfielder dragged his effort into the side netting.
Mason Bennett spurned a glorious chance to make the points safe late on for Derby but Camp pulled off a fine save from his left-footed angled drive.