The lead changed hands six times in an entertaining game, but it was the Yorkshire side who edged to a five-point victory which leaves them third bottom with two matches remaining.
Two penalties from scrum-half Isaac Green and a conversion following Ed Falkingham’s try left Ionians narrowly trailing at 15-13 at the break.
Further tries from Ali Thomson and Steve Slingsby were both converted by Green as the visitors edged into a 27-22 lead.
Rosslyn Park hit back with a converted try of their own late in the game, but there was just time for Green to kick a penalty which gave his side the win.
A seven-try performance gave Harrogate a 45-32 victory at Preston Grasshoppers in National Two North.
But they had to fight back from behind with Keane Naylor and former Yorkshire Carnegie winger David Doherty scoring their only first half tries with Grasshoppers leading 25-12 at the break.
Fly-half Sam Fox and second row Sam Brady saw their tries converted by Doherty as they took a 26-25 lead, and others followed from centre Ben Dixon, replacement Oli Rosillo and winger Luke Edwards, Doherty converting two of those last three.
Sheffield Tigers had to settle for two bonus points from their away game as hosts Tynedale ran out 41-40 winners.
Tigers led 23-14 at half time with tries coming from Liam Wallace and Pete Swatkins, while Mark Ireland kicked both conversions as well as three penalties.
After the break Lee Monks scored twice more for Tigers and Ireland added the extras, but Tynedale ran in three more tries and added two conversions to edge to a last-minute win and leave Tigers still chasing points to avoid the drop.
Elsewhere, Wharfedale took a losing bonus point from their 22-15 loss at Chester, while Otley were beaten 65-17 at home by Leicester Lions.
Sheffield’s promotion push continued as they beat Birmingham and Solihull 32-5 at Abbeydale in National Three Midlands.
No 8 Jonny France’s first half try was converted by Andy Hodgson, who also added a penalty to help Sheffield to a 10-5 lead at the break.
After half time centre Rupert Broadley scored twice, while winger Owen Smith also touched down and Hodgson kicked two conversions and a penalty.
Hull ran out easy 59-15 winners over Doncaster Phoenix, with scrum-half Harvey Harding scoring a hat-trick and winger Tomasi Tanumi scoring two.
Others came from hooker Tom Wright, full-back Lee Birch and sub Liam Regardsoe, while Tyler Price kicked seven conversions.
Morley’s bid to avoid relegation received a boost when they beat Lymm 41-30, while champions Huddersfield beat title rivals Rossendale 41-11.
Sandal were 66-17 winners over relegation-threatened Waterloo, while Ilkley secured a big 49-5 win over Stockport, who are already relegated.
And five tries wasn’t enough for Cleckheaton who lost out 52-31 at home against Wirral.
Pocklington’s promotion from North One East is almost confirmed after they won 50-10 against Huddersfield YMCA. With two matches left, they need just one point to confirm the title.
Driffield were 32-29 winners at Alnwick, with Joe Robinson and Ben Dinsdale scoring twice each, Adam Brankley scoring the other.
Elsewhere, Malton and Norton secured a close 20-17 win at Morpeth, while Dinnington ran in five tries on their way to a 45-19 win over Guisborough.
West Leeds were 31-28 winners over Keighley as their Yorkshire One promotion push continued.
Tries came from Danny Booth, Henry Rust and Stephan James, while Dale Breakwell kicked three conversions and a penalty.
Champions Bridlington were 62-0 winners at home against North Ribblesdale.